Phase 5: detail screens (scrollable lists + back button) + main controller

- weather_detail: scrollable hourly forecast (time, temp, description,
  rain probability), data logic ported from old weather_detail_screen.cpp
- calendar_detail: scrollable list of all 10 events (summary + formatted
  date/all_day), ported from old calendar_detail_screen.cpp
- mvg: scrollable departures list (line badge U/S colored, destination,
  time/delay, cancellation), 1-minute refresh timer ported from old
  mvg_screen.cpp
- all three use back_button widget (fixed bottom-left)
- main.cpp: Screen controller, navigates between screens via callbacks,
  5-minute inactivity timeout -> home, per-screen tick() for refresh

src/main.cpp

@@ -4,13 +4,27 @@
 #include <secrets.h>
 #include <theme.h>
 #include "display/display_setup.h"
-#include "api/weather_api.h"
-#include "api/calendar_api.h"
-#include "api/departures_api.h"
+#include "ui/screen_base.h"
+#include "ui/home_screen.h"
+#include "ui/weather_detail_screen.h"
+#include "ui/calendar_detail_screen.h"
+#include "ui/mvg_screen.h"
 
 namespace {
 
 unsigned long lastTickMs = 0;
+unsigned long lastInteractionMs = 0;
+const unsigned long IDLE_TIMEOUT_MS = 5UL * 60UL * 1000UL;
+
+Screen screens[4];
+ScreenId current = ScreenId::HOME;
+
+ScreenId navigate(ScreenId target) {
+    lastInteractionMs = millis();
+    current = target;
+    screens[(int)target].show();
+    return target;
+}
 
 void connectWifi() {
     Serial.println("Verbinde mit WLAN...");
@@ -30,65 +44,6 @@ void connectWifi() {
     }
 }
 
-// Phase 2 verification: fetch all three APIs once at boot and dump parsed
-// fields to Serial so JSON parsing can be verified independently of the UI.
-void verifyApisViaSerial() {
-    Serial.println("\n=== Wetter ===");
-    WeatherData w = fetchWeather();
-    Serial.printf("valid=%d temp=%d symbol=%s desc=%s forecast=%u\n",
-                  w.valid, w.current.temperature,
-                  w.current.symbol.c_str(), w.current.description.c_str(),
-                  w.forecast.size());
-    for (size_t i = 0; i < w.forecast.size() && i < 3; ++i) {
-        const auto &f = w.forecast[i];
-        Serial.printf("  [%u] %s %dC %s precip=%.2f/%s\n", i, f.time.c_str(),
-                      f.temperature, f.description.c_str(),
-                      f.precipitationProbability, f.precipitationType.c_str());
-    }
-
-    Serial.println("\n=== Kalender ===");
-    CalendarData c = fetchCalendar();
-    Serial.printf("valid=%d events=%u\n", c.valid, c.events.size());
-    for (size_t i = 0; i < c.events.size() && i < 3; ++i) {
-        const auto &e = c.events[i];
-        Serial.printf("  [%u] %s | %s all_day=%d\n", i, e.summary.c_str(),
-                      e.startAt.c_str(), e.allDay);
-    }
-
-    Serial.println("\n=== MVG ===");
-    DeparturesData d = fetchDepartures();
-    Serial.printf("valid=%d departures=%u\n", d.valid, d.departures.size());
-    for (size_t i = 0; i < d.departures.size() && i < 3; ++i) {
-        const auto &dep = d.departures[i];
-        Serial.printf("  [%u] %s %s -> %s %s delay=%d cancel=%d\n", i,
-                      dep.type.c_str(), dep.line.c_str(),
-                      dep.destination.c_str(), dep.timeStr.c_str(),
-                      dep.delayMin, dep.cancelled);
-    }
-    Serial.println("=== API verification done ===\n");
-}
-
-void btn_event_cb(lv_event_t *e) {
-    lv_obj_t *label = (lv_obj_t *)lv_event_get_user_data(e);
-    static int n = 0;
-    lv_label_set_text_fmt(label, "Taps: %d", ++n);
-}
-
-void buildTestScreen() {
-    lv_obj_t *scr = lv_screen_active();
-    lv_obj_set_style_bg_color(scr, Theme::bg(), 0);
-
-    lv_obj_t *btn = lv_button_create(scr);
-    lv_obj_set_size(btn, 200, 80);
-    lv_obj_center(btn);
-    lv_obj_set_style_bg_color(btn, Theme::accentWeather(), 0);
-
-    lv_obj_t *label = lv_label_create(btn);
-    lv_label_set_text(label, "Taps: 0");
-    lv_obj_center(label);
-    lv_obj_add_event_cb(btn, btn_event_cb, LV_EVENT_CLICKED, label);
-}
-
 } // namespace
 
 void setup() {
@@ -97,8 +52,19 @@ void setup() {
     Serial.println("WT32-SC01 Plus booting...");
     display_init();
     connectWifi();
-    verifyApisViaSerial();
-    buildTestScreen();
+
+    // Build all four screens and wire navigation callbacks.
+    screens[(int)ScreenId::HOME]            = homeScreen_make();
+    screens[(int)ScreenId::WEATHER_DETAIL]  = weatherDetailScreen_make();
+    screens[(int)ScreenId::CALENDAR_DETAIL] = calendarDetailScreen_make();
+    screens[(int)ScreenId::MVG]             = mvgScreen_make();
+    homeScreen_setNavigator(navigate);
+    weatherDetailScreen_setNavigator(navigate);
+    calendarDetailScreen_setNavigator(navigate);
+    mvgScreen_setNavigator(navigate);
+
+    lastInteractionMs = millis();
+    navigate(ScreenId::HOME);
     Serial.println("Setup done.");
 }
 
@@ -107,5 +73,12 @@ void loop() {
     if (now - lastTickMs >= 5) {
         lastTickMs = now;
         display_loop();
+        screens[(int)current].tick();
+
+        // Inactivity: return to home after 5 minutes without input.
+        if (current != ScreenId::HOME &&
+            now - lastInteractionMs >= IDLE_TIMEOUT_MS) {
+            navigate(ScreenId::HOME);
+        }
     }
 }

src/ui/calendar_detail_screen.cpp

@@ -0,0 +1,77 @@
+#include "calendar_detail_screen.h"
+#include "ui/widgets/back_button.h"
+#include "api/calendar_api.h"
+#include <theme.h>
+#include <text_utils.h>
+#include <date_utils.h>
+#include <lvgl.h>
+
+namespace {
+
+ScreenId (*g_navigate)(ScreenId) = nullptr;
+void on_back(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::HOME); }
+
+CalendarData lastCalendar;
+bool ok = false;
+lv_obj_t *list = nullptr;
+
+void buildList() {
+    if (!list) return;
+    lv_obj_clean(list);
+
+    if (!ok) {
+        lv_obj_t *lbl = lv_label_create(list);
+        lv_label_set_text(lbl, LV_SYMBOL_WARNING " Keine Verbindung");
+        lv_obj_set_style_text_color(lbl, Theme::accentError(), 0);
+        return;
+    }
+
+    for (const auto &ev : lastCalendar.events) {
+        lv_obj_t *row = lv_obj_create(list);
+        lv_obj_set_size(row, 280, LV_SIZE_CONTENT);
+        lv_obj_set_style_bg_opa(row, LV_OPA_TRANSP, 0);
+        lv_obj_set_style_border_width(row, 0, 0);
+        lv_obj_set_style_pad_all(row, 6, 0);
+        lv_obj_clear_flag(row, LV_OBJ_FLAG_SCROLLABLE);
+
+        lv_obj_t *sum = lv_label_create(row);
+        lv_label_set_text(sum, sanitizeGermanText(ev.summary.substring(0, 30)).c_str());
+        lv_obj_set_style_text_color(sum, Theme::text(), 0);
+        lv_obj_align(sum, LV_ALIGN_TOP_LEFT, 0, 0);
+
+        lv_obj_t *when = lv_label_create(row);
+        lv_label_set_text(when, DateUtils::formatShortDE(ev.startAt, ev.allDay).c_str());
+        lv_obj_set_style_text_color(when, Theme::accentCalendar(), 0);
+        lv_obj_align(when, LV_ALIGN_TOP_LEFT, 0, 20);
+    }
+}
+
+} // namespace
+
+void calendarDetailScreen_setNavigator(ScreenId (*nav)(ScreenId)) { g_navigate = nav; }
+
+void calendarDetailScreen_create(Screen &s) {
+    list = lv_list_create(s.root);
+    lv_obj_set_pos(list, 0, 0);
+    lv_obj_set_size(list, 320, 480 - 80);
+    lv_obj_set_style_bg_color(list, Theme::bg(), 0);
+    lv_obj_set_style_border_width(list, 0, 0);
+    back_button_create(s.root, on_back, nullptr);
+}
+
+void calendarDetailScreen_refresh(Screen &) {
+    CalendarData c = fetchCalendar();
+    ok = c.valid;
+    if (c.valid) lastCalendar = c;
+    buildList();
+}
+
+void calendarDetailScreen_tick(Screen &) {}
+
+Screen calendarDetailScreen_make() {
+    Screen s;
+    s.create_fn  = calendarDetailScreen_create;
+    s.refresh_fn = calendarDetailScreen_refresh;
+    s.tick_fn    = calendarDetailScreen_tick;
+    return s;
+}

src/ui/calendar_detail_screen.h

@@ -0,0 +1,6 @@
+#pragma once
+#include "ui/screen_base.h"
+
+// Calendar detail: scrollable list of all 10 events + back button.
+Screen calendarDetailScreen_make();
+void calendarDetailScreen_setNavigator(ScreenId (*nav)(ScreenId));

src/ui/mvg_screen.cpp

@@ -0,0 +1,105 @@
+#include "mvg_screen.h"
+#include "ui/widgets/back_button.h"
+#include "api/departures_api.h"
+#include <theme.h>
+#include <text_utils.h>
+#include <lvgl.h>
+
+namespace {
+
+ScreenId (*g_navigate)(ScreenId) = nullptr;
+void on_back(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::HOME); }
+
+DeparturesData lastData;
+bool ok = false;
+lv_obj_t *list = nullptr;
+unsigned long lastFetchMs = 0;
+const unsigned long REFRESH_INTERVAL_MS = 60UL * 1000UL;
+
+void buildList() {
+    if (!list) return;
+    lv_obj_clean(list);
+
+    if (!ok) {
+        lv_obj_t *lbl = lv_label_create(list);
+        lv_label_set_text(lbl, LV_SYMBOL_WARNING " Keine Verbindung");
+        lv_obj_set_style_text_color(lbl, Theme::accentError(), 0);
+        return;
+    }
+
+    for (const auto &dep : lastData.departures) {
+        lv_obj_t *row = lv_obj_create(list);
+        lv_obj_set_size(row, 280, LV_SIZE_CONTENT);
+        lv_obj_set_style_bg_opa(row, LV_OPA_TRANSP, 0);
+        lv_obj_set_style_border_width(row, 0, 0);
+        lv_obj_set_style_pad_all(row, 6, 0);
+        lv_obj_clear_flag(row, LV_OBJ_FLAG_SCROLLABLE);
+
+        // Line badge (colored text: U red, S green).
+        String badge = String(dep.icon) + " " + dep.line;
+        lv_obj_t *ln = lv_label_create(row);
+        lv_label_set_text(ln, badge.c_str());
+        lv_obj_set_style_text_color(ln,
+            dep.type == "UBAHN" ? Theme::accentUBahn() : Theme::accentSBahn(), 0);
+        lv_obj_align(ln, LV_ALIGN_TOP_LEFT, 0, 0);
+
+        String dest = sanitizeGermanText(dep.destination.substring(0, 20));
+        lv_obj_t *d = lv_label_create(row);
+        lv_label_set_text(d, dest.c_str());
+        lv_obj_set_style_text_color(d, Theme::text(), 0);
+        lv_obj_align(d, LV_ALIGN_TOP_LEFT, 0, 18);
+
+        String right;
+        if (dep.cancelled) {
+            right = "Ausfall";
+        } else {
+            right = dep.timeStr;
+            if (dep.delayMin > 0) right += " +" + String(dep.delayMin);
+        }
+        lv_obj_t *t = lv_label_create(row);
+        lv_label_set_text(t, right.c_str());
+        lv_obj_set_style_text_color(t,
+            dep.cancelled ? Theme::accentError() : Theme::text(), 0);
+        lv_obj_align(t, LV_ALIGN_TOP_RIGHT, 0, 18);
+    }
+}
+
+void doFetch() {
+    DeparturesData d = fetchDepartures();
+    ok = d.valid;
+    if (d.valid) lastData = d;
+    lastFetchMs = millis();
+}
+
+} // namespace
+
+void mvgScreen_setNavigator(ScreenId (*nav)(ScreenId)) { g_navigate = nav; }
+
+void mvgScreen_create(Screen &s) {
+    list = lv_list_create(s.root);
+    lv_obj_set_pos(list, 0, 0);
+    lv_obj_set_size(list, 320, 480 - 80);
+    lv_obj_set_style_bg_color(list, Theme::bg(), 0);
+    lv_obj_set_style_border_width(list, 0, 0);
+    back_button_create(s.root, on_back, nullptr);
+}
+
+void mvgScreen_refresh(Screen &) {
+    doFetch();
+    buildList();
+}
+
+void mvgScreen_tick(Screen &) {
+    if (lastFetchMs == 0 || millis() - lastFetchMs >= REFRESH_INTERVAL_MS) {
+        doFetch();
+        buildList();
+    }
+}
+
+Screen mvgScreen_make() {
+    Screen s;
+    s.create_fn  = mvgScreen_create;
+    s.refresh_fn = mvgScreen_refresh;
+    s.tick_fn    = mvgScreen_tick;
+    return s;
+}

src/ui/mvg_screen.h

@@ -0,0 +1,6 @@
+#pragma once
+#include "ui/screen_base.h"
+
+// MVG departures: scrollable list of all departures + back button.
+Screen mvgScreen_make();
+void mvgScreen_setNavigator(ScreenId (*nav)(ScreenId));

src/ui/weather_detail_screen.cpp

@@ -0,0 +1,95 @@
+#include "weather_detail_screen.h"
+#include "ui/widgets/back_button.h"
+#include "api/weather_api.h"
+#include <theme.h>
+#include <text_utils.h>
+#include <lvgl.h>
+
+namespace {
+
+ScreenId (*g_navigate)(ScreenId) = nullptr;
+void on_back(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::HOME); }
+
+WeatherData lastWeather;
+bool ok = false;
+lv_obj_t *list = nullptr;
+
+void buildList() {
+    if (!list) return;
+    lv_obj_clean(list);
+
+    if (!ok) {
+        lv_obj_t *lbl = lv_label_create(list);
+        lv_label_set_text(lbl, LV_SYMBOL_WARNING " Keine Verbindung");
+        lv_obj_set_style_text_color(lbl, Theme::accentError(), 0);
+        return;
+    }
+
+    // Header row with current conditions.
+    String header = String(lastWeather.current.temperature) + " C  " +
+                    sanitizeGermanText(lastWeather.current.description);
+    lv_obj_t *h = lv_label_create(list);
+    lv_label_set_text(h, header.c_str());
+    lv_obj_set_style_text_font(h, &lv_font_montserrat_20, 0);
+    lv_obj_set_style_text_color(h, Theme::text(), 0);
+
+    for (const auto &fe : lastWeather.forecast) {
+        lv_obj_t *row = lv_obj_create(list);
+        lv_obj_set_size(row, 280, LV_SIZE_CONTENT);
+        lv_obj_set_style_bg_opa(row, LV_OPA_TRANSP, 0);
+        lv_obj_set_style_border_width(row, 0, 0);
+        lv_obj_set_style_pad_all(row, 6, 0);
+        lv_obj_clear_flag(row, LV_OBJ_FLAG_SCROLLABLE);
+
+        // time hh:mm
+        int tIdx = fe.time.indexOf('T');
+        String hhmm = tIdx > 0 ? fe.time.substring(tIdx + 1, tIdx + 6) : fe.time;
+
+        String left = hhmm + "  " + String(fe.temperature) + "C";
+        lv_obj_t *l = lv_label_create(row);
+        lv_label_set_text(l, left.c_str());
+        lv_obj_set_style_text_color(l, Theme::text(), 0);
+        lv_obj_align(l, LV_ALIGN_TOP_LEFT, 0, 0);
+
+        String desc = sanitizeGermanText(fe.description.substring(0, 16));
+        if (fe.precipitationType == "rain" && fe.precipitationProbability > 0.0f) {
+            char buf[8];
+            snprintf(buf, sizeof(buf), " %.0f%%", fe.precipitationProbability * 100);
+            desc += buf;
+        }
+        lv_obj_t *d = lv_label_create(row);
+        lv_label_set_text(d, desc.c_str());
+        lv_obj_set_style_text_color(d, Theme::textDim(), 0);
+        lv_obj_align(d, LV_ALIGN_TOP_LEFT, 0, 18);
+    }
+}
+
+} // namespace
+
+void weatherDetailScreen_setNavigator(ScreenId (*nav)(ScreenId)) { g_navigate = nav; }
+
+void weatherDetailScreen_create(Screen &s) {
+    list = lv_list_create(s.root);
+    lv_obj_set_pos(list, 0, 0);
+    lv_obj_set_size(list, 320, 480 - 80);
+    lv_obj_set_style_bg_color(list, Theme::bg(), 0);
+    lv_obj_set_style_border_width(list, 0, 0);
+    back_button_create(s.root, on_back, nullptr);
+}
+
+void weatherDetailScreen_refresh(Screen &) {
+    WeatherData w = fetchWeather();
+    ok = w.valid;
+    if (w.valid) lastWeather = w;
+    buildList();
+}
+
+void weatherDetailScreen_tick(Screen &) {}
+
+Screen weatherDetailScreen_make() {
+    Screen s;
+    s.create_fn  = weatherDetailScreen_create;
+    s.refresh_fn = weatherDetailScreen_refresh;
+    s.tick_fn    = weatherDetailScreen_tick;
+    return s;
+}

src/ui/weather_detail_screen.h

@@ -0,0 +1,6 @@
+#pragma once
+#include "ui/screen_base.h"
+
+// Weather detail: scrollable hourly forecast list + back button.
+Screen weatherDetailScreen_make();
+void weatherDetailScreen_setNavigator(ScreenId (*nav)(ScreenId));