Phase 0: minimal main.cpp (WiFi + display + LVGL test button) + carry over hardware-independent helpers

- src/main.cpp rewritten for ESP32-S3: Serial + display_init + WiFi
  connect (logic ported from old main.cpp, M5.Lcd prints -> Serial),
  LVGL test button screen to verify touch in Phase 1
- include/text_utils.h, date_utils.h: kept 1:1 (no M5Stack dependency)
- include/secrets.h.example, .gitignore, scripts/{build,deploy}.sh,
  .github/workflows/build.yml: kept 1:1 (hardware-independent)

.github/workflows/build.yml

@@ -0,0 +1,24 @@
+name: PlatformIO CI
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cache/pip
+            ~/.platformio/.cache
+          key: ${{ runner.os }}-pio
+      - name: Install PlatformIO Core
+        run: pip install --upgrade platformio
+      - name: Generate placeholder secrets.h for CI build
+        run: cp include/secrets.h.example include/secrets.h
+      - name: Build PlatformIO Project
+        run: pio run

.gitignore

@@ -0,0 +1,7 @@
+.pio/
+.vscode/
+include/secrets.h
+*.o
+*.bin
+
+.venv-platformio/

include/date_utils.h

@@ -0,0 +1,66 @@
+#pragma once
+#include <Arduino.h>
+
+// No NTP/network time used, purely computed from date strings coming from
+// the calendar API itself, as specified.
+namespace DateUtils {
+
+inline const char *weekdayShortDE(int isoWeekday /* 0=Mon..6=Sun */) {
+    static const char *names[7] = {"Mo", "Di", "Mi", "Do", "Fr", "Sa", "So"};
+    if (isoWeekday < 0 || isoWeekday > 6) return "??";
+    return names[isoWeekday];
+}
+
+// Sakamoto's algorithm, returns 0=Monday..6=Sunday
+inline int computeWeekdayMonBased(int year, int month, int day) {
+    static const int t[] = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4};
+    int y = year;
+    if (month < 3) y -= 1;
+    int w = (y + y / 4 - y / 100 + y / 400 + t[month - 1] + day) % 7; // 0=Sun
+    return (w + 6) % 7; // convert to 0=Mon
+}
+
+struct ParsedDateTime {
+    bool valid = false;
+    int year = 0, month = 0, day = 0, hour = 0, minute = 0;
+};
+
+inline ParsedDateTime parseIso(const String &iso) {
+    ParsedDateTime r;
+    if (iso.length() < 10) return r;
+
+    int y = iso.substring(0, 4).toInt();
+    int mo = iso.substring(5, 7).toInt();
+    int d = iso.substring(8, 10).toInt();
+
+    int h = 0, mi = 0;
+    int tIdx = iso.indexOf('T');
+    if (tIdx > 0 && iso.length() >= tIdx + 6) {
+        h = iso.substring(tIdx + 1, tIdx + 3).toInt();
+        mi = iso.substring(tIdx + 4, tIdx + 6).toInt();
+    }
+
+    if (y == 0 || mo == 0 || d == 0) return r;
+
+    r.valid = true;
+    r.year = y; r.month = mo; r.day = d; r.hour = h; r.minute = mi;
+    return r;
+}
+
+// "Mo 3.8. 14:00" for timed events, "Mo 3.8." for all-day events.
+inline String formatShortDE(const String &iso, bool allDay) {
+    ParsedDateTime p = parseIso(iso);
+    if (!p.valid) return iso;
+
+    int wd = computeWeekdayMonBased(p.year, p.month, p.day);
+    String out = String(weekdayShortDE(wd)) + " " + String(p.day) + "." + String(p.month) + ".";
+
+    if (!allDay) {
+        char buf[8];
+        snprintf(buf, sizeof(buf), " %02d:%02d", p.hour, p.minute);
+        out += buf;
+    }
+    return out;
+}
+
+} // namespace DateUtils

include/secrets.h.example

@@ -0,0 +1,11 @@
+#pragma once
+
+// Copy this file to secrets.h and fill in your real values.
+// secrets.h is git-ignored and must never be committed.
+
+#define WIFI_SSID "YOUR_WIFI_SSID"
+#define WIFI_PASSWORD "YOUR_WIFI_PASSWORD"
+
+#define WEATHER_API_URL "http://<host>:<port>/api/weather"
+#define CALENDAR_API_URL "http://<host>:<port>/api/events"
+#define DEPARTURES_API_URL "http://<host>:<port>/api/departures"

include/text_utils.h

@@ -0,0 +1,27 @@
+#pragma once
+#include <Arduino.h>
+
+// M5Stack default font can't render UTF-8 German umlauts correctly.
+// Transliterate them to ASCII before printing.
+inline String sanitizeGermanText(const String &input) {
+    String out;
+    out.reserve(input.length());
+    for (size_t i = 0; i < input.length(); i++) {
+        unsigned char c1 = input[i];
+        if (c1 == 0xC3 && i + 1 < input.length()) {
+            unsigned char c2 = input[i + 1];
+            switch (c2) {
+                case 0xA4: out += "ae"; i++; continue;
+                case 0xB6: out += "oe"; i++; continue;
+                case 0xBC: out += "ue"; i++; continue;
+                case 0x84: out += "Ae"; i++; continue;
+                case 0x96: out += "Oe"; i++; continue;
+                case 0x9C: out += "Ue"; i++; continue;
+                case 0x9F: out += "ss"; i++; continue;
+                default: break;
+            }
+        }
+        out += (char)c1;
+    }
+    return out;
+}

scripts/build.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")/.."
+VENV_DIR=".venv-platformio"
+if [ ! -d "$VENV_DIR" ]; then
+    echo "Creating local virtualenv in $VENV_DIR ..."
+    python3 -m venv "$VENV_DIR"
+    "$VENV_DIR/bin/pip" install --upgrade pip
+    "$VENV_DIR/bin/pip" install platformio
+fi
+echo "Running build (no upload) ..."
+"$VENV_DIR/bin/pio" run
+echo "Build finished successfully."

scripts/deploy.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+cd "$(dirname "$0")/.."
+VENV_DIR=".venv-platformio"
+if [ ! -d "$VENV_DIR" ]; then
+    echo "Creating local virtualenv in $VENV_DIR ..."
+    python3 -m venv "$VENV_DIR"
+    "$VENV_DIR/bin/pip" install --upgrade pip
+    "$VENV_DIR/bin/pip" install platformio
+fi
+PIO="$VENV_DIR/bin/pio"
+if [ "$#" -ge 1 ]; then
+    PORT="$1"
+    echo "Using forced upload port: $PORT"
+    "$PIO" run --target upload --upload-port "$PORT"
+else
+    echo "Auto-detecting upload port..."
+    "$PIO" run --target upload
+fi
+echo "Build + flash complete."

src/main.cpp

@@ -0,0 +1,69 @@
+#include <Arduino.h>
+#include <WiFi.h>
+#include <lvgl.h>
+#include <secrets.h>
+#include <theme.h>
+#include "display/display_setup.h"
+
+namespace {
+
+unsigned long lastTickMs = 0;
+
+void connectWifi() {
+    Serial.println("Verbinde mit WLAN...");
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
+    unsigned long start = millis();
+    while (WiFi.status() != WL_CONNECTED && millis() - start < 15000) {
+        delay(300);
+        Serial.print(".");
+    }
+    Serial.println();
+    if (WiFi.status() == WL_CONNECTED) {
+        Serial.print("WLAN verbunden, IP: ");
+        Serial.println(WiFi.localIP());
+    } else {
+        Serial.println("WLAN fehlgeschlagen");
+    }
+}
+
+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() {
+    Serial.begin(115200);
+    delay(200);
+    Serial.println("WT32-SC01 Plus booting...");
+    display_init();
+    connectWifi();
+    buildTestScreen();
+    Serial.println("Setup done.");
+}
+
+void loop() {
+    unsigned long now = millis();
+    if (now - lastTickMs >= 5) {
+        lastTickMs = now;
+        display_loop();
+    }
+}