feat(doorbell): add staged boot sequence and refactor main loop

libraries/KlubhausCore/src/Config.h

@@ -22,6 +22,11 @@
 #define HINT_MIN_BRIGHTNESS 30
 #define HINT_MAX_BRIGHTNESS 60
 
+// ── Loop yield (prevents Task Watchdog on ESP32) ──
+#ifndef LOOP_YIELD_MS
+#define LOOP_YIELD_MS 10
+#endif
+
 // ── WiFi credential struct (populated in each board's secrets.h) ──
 struct WiFiCred {
     const char* ssid;