Phase 4: home screen with three touch tiles

- weather tile (big, top, accent blue): temperature + description +
  rain hint badge, tap -> weather detail
- calendar tile (big, middle, accent purple): first 2 events as preview
  (summary + DateUtils::formatShortDE incl. all_day handling), tap ->
  calendar detail
- mvg tile (small, bottom, accent green): label only, no preview,
  tap -> mvg screen
- 10-minute refresh timer + tick() check (ported from old home_screen.cpp)
- data logic reused verbatim: doFetch/weatherOk/calendarOk pattern,
  willRainSoon threshold, sanitizeGermanText + formatShortDE formatting
- placeholder glyphs (LV_SYMBOL_IMAGE/LIST/FILE) until bitmap icons
  land in Phase 6

src/ui/home_screen.cpp

@@ -0,0 +1,129 @@
+#include "home_screen.h"
+#include "ui/widgets/tile_button.h"
+#include "api/weather_api.h"
+#include "api/calendar_api.h"
+#include <theme.h>
+#include <text_utils.h>
+#include <date_utils.h>
+#include <lvgl.h>
+
+namespace {
+
+// --- navigation callback target (set by main.cpp) ---
+ScreenId (*g_navigate)(ScreenId) = nullptr;
+
+void on_weather_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::WEATHER_DETAIL); }
+void on_calendar_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::CALENDAR_DETAIL); }
+void on_mvg_tile(lv_event_t *) { if (g_navigate) g_navigate(ScreenId::MVG); }
+
+// --- cached data + refresh timer (ported from old home_screen.cpp) ---
+WeatherData lastWeather;
+CalendarData lastCalendar;
+bool weatherOk = false;
+bool calendarOk = false;
+unsigned long lastFetchMs = 0;
+const unsigned long REFRESH_INTERVAL_MS = 10UL * 60UL * 1000UL;
+
+// --- tile handles (value labels, for updating without rebuild) ---
+TileButton weatherTile{};
+TileButton calendarTile{};
+TileButton mvgTile{};
+bool widgetsBuilt = false;
+
+void doFetch() {
+    WeatherData w = fetchWeather();
+    weatherOk = w.valid;
+    if (w.valid) lastWeather = w;
+    CalendarData c = fetchCalendar();
+    calendarOk = c.valid;
+    if (c.valid) lastCalendar = c;
+    lastFetchMs = millis();
+}
+
+// --- formatting helpers (ported from old home_screen.cpp rendering) ---
+
+String weatherIconGlyph(const String &symbol) {
+    // Phase 4 placeholder: map symbol condition to a unicode glyph until
+    // bitmap icons land in Phase 6. m=night, condition char = symbol[1].
+    (void)symbol;
+    return LV_SYMBOL_IMAGE; // cloud/weather placeholder; bitmaps come in Phase 6
+}
+
+String formatWeatherValue(const WeatherData &w) {
+    if (!w.valid) return "Wetter n.a.";
+    String s = String(w.current.temperature) + " C";
+    s += "\n" + sanitizeGermanText(w.current.description);
+    if (willRainSoon(w, 8)) s += "\n[Regen moeglich]";
+    return s;
+}
+
+String formatCalendarPreview(const CalendarData &c) {
+    if (!c.valid) return "Kalender n.a.";
+    String s;
+    int shown = 0;
+    for (const auto &ev : c.events) {
+        if (shown >= 2) break;
+        if (shown > 0) s += "\n";
+        s += sanitizeGermanText(ev.summary.substring(0, 22));
+        s += "\n" + DateUtils::formatShortDE(ev.startAt, ev.allDay);
+        ++shown;
+    }
+    if (s.length() == 0) s = "Keine Termine";
+    return s;
+}
+
+void updateWidgets() {
+    if (!widgetsBuilt) return;
+    tile_button_set_value(weatherTile, formatWeatherValue(lastWeather).c_str());
+    tile_button_set_icon(weatherTile, weatherIconGlyph(lastWeather.current.symbol).c_str());
+    tile_button_set_value(calendarTile, formatCalendarPreview(lastCalendar).c_str());
+    tile_button_set_icon(calendarTile, LV_SYMBOL_FILE);
+    tile_button_set_value(mvgTile, "");
+    tile_button_set_icon(mvgTile, LV_SYMBOL_LIST);
+}
+
+} // namespace
+
+Screen homeScreen;
+
+void homeScreen_setNavigator(Navigator nav) {
+    g_navigate = nav;
+}
+
+void homeScreen_create(Screen &s) {
+    // Layout (portrait 320x480):
+    //  weather tile   x=12 y=12  w=296 h=170  (big, top)
+    //  calendar tile  x=12 y=194 w=296 h=170  (big, middle, with 2-event preview)
+    //  mvg tile       x=12 y=376 w=296 h=92   (small, bottom, no preview)
+    weatherTile  = tile_button_create(s.root, 12, 12,  296, 170,
+                                      Theme::accentWeather(), "Wetter",
+                                      on_weather_tile, nullptr);
+    calendarTile = tile_button_create(s.root, 12, 194, 296, 170,
+                                      Theme::accentCalendar(), "Termine",
+                                      on_calendar_tile, nullptr);
+    mvgTile      = tile_button_create(s.root, 12, 376, 296, 92,
+                                      Theme::accentMvg(), "MVG",
+                                      on_mvg_tile, nullptr);
+    widgetsBuilt = true;
+}
+
+void homeScreen_refresh(Screen &) {
+    doFetch();
+    updateWidgets();
+}
+
+void homeScreen_tick(Screen &) {
+    if (lastFetchMs == 0 || millis() - lastFetchMs >= REFRESH_INTERVAL_MS) {
+        doFetch();
+        updateWidgets();
+    }
+}
+
+Screen homeScreen_make() {
+    Screen s;
+    s.create_fn  = homeScreen_create;
+    s.refresh_fn = homeScreen_refresh;
+    s.tick_fn    = homeScreen_tick;
+    return s;
+}
+

src/ui/home_screen.h

@@ -0,0 +1,17 @@
+#pragma once
+#include "ui/screen_base.h"
+
+// Home screen: three touch tiles (weather big, calendar big w/ 2 events,
+// mvg small). Tap navigates to the respective detail screen.
+
+// Navigation callback type: called with the target ScreenId, returns the
+// actually-shown ScreenId (so main.cpp can drive transitions + inactivity).
+using Navigator = ScreenId (*)(ScreenId);
+
+// Build the home screen object (does not create widgets until show()).
+Screen homeScreen_make();
+
+// Set the navigation callback (called by main.cpp once at startup).
+void homeScreen_setNavigator(Navigator nav);
+
+extern Screen homeScreen;