feat: LVGL 9.5 upgrade, FTP server, premium AMOLED UI

- Upgraded LVGL from 8.4 to 9.5.0 (new display/input API)
- Rewrote DisplayManager for LVGL 9 (lv_display_create, tick callback)
- New lv_conf.h for v9.5 with optimized widget selection
- Premium dark AMOLED UI with gradient panels, status dots, storage bar
- Backend: Wi-Fi from SD JSON, NTP Vienna, SimpleFTPServer on SD_MMC
- Removed 6 unused sensor libs, added ArduinoJson + SimpleFTPServer
- Build: 19% RAM, 4.6% Flash — verified compilation success

src/main.cpp

@@ -161,7 +161,7 @@ void ftpTransferCallback(FtpTransferOperation ftpOperation, const char *name, ui
 //  Time display
 // ---------------------------------------------------------------------------
 
-/** Update the UI time label once per second */
+/** Update the UI time and date labels once per second */
 static void updateTimeDisplay() {
     unsigned long now = millis();
     if (now - last_time_update < 1000) return;
@@ -172,6 +172,10 @@ static void updateTimeDisplay() {
         char buf[16];
         strftime(buf, sizeof(buf), "%H:%M:%S", &timeinfo);
         ui_set_time(buf);
+
+        char datebuf[32];
+        strftime(datebuf, sizeof(datebuf), "%a, %d %b %Y", &timeinfo);
+        ui_set_date(datebuf);
     }
 }