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)

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();
+    }
+}