Person detection via direct MQTT instead of HA entities

- Electron main process subscribes to Frigate's MQTT topics
  (frigate/<camera>/person and frigate/events) directly via mqtt.js,
  bypassing the broken HA MQTT integration
- Watched cameras: Front_Porch, FPE, Porch_Downstairs, Driveway_door
- On person detection, exits photo-frame idle and shows full-screen
  camera feed for 30 seconds
- Removed HA entity-based person detection code (entityToCameraName,
  personDetectionEntities config dependency)
- Deleted unused useFrigateDetection HTTP polling hook (superseded)

electron/preload.ts

@@ -16,6 +16,7 @@ export interface ElectronAPI {
   frigate: {
     startStream: (rtspUrl: string) => Promise<boolean>;
     stopStream: () => Promise<boolean>;
+    onPersonDetected: (callback: (camera: string) => void) => () => void;
   };
   app: {
     quit: () => void;
@@ -57,6 +58,11 @@ const electronAPI: ElectronAPI = {
   frigate: {
     startStream: (rtspUrl: string) => ipcRenderer.invoke('frigate:startStream', rtspUrl),
     stopStream: () => ipcRenderer.invoke('frigate:stopStream'),
+    onPersonDetected: (callback: (camera: string) => void) => {
+      const handler = (_event: IpcRendererEvent, camera: string) => callback(camera);
+      ipcRenderer.on('frigate:personDetected', handler);
+      return () => ipcRenderer.removeListener('frigate:personDetected', handler);
+    },
   },
   app: {
     quit: () => ipcRenderer.invoke('app:quit'),