Fix streaming: MSE-first with go2rtc init protocol

- Switch from WebRTC-first to MSE-first streaming (more reliable
  across all camera types including high-res IP cameras)
- Send required {"type":"mse"} init message to go2rtc WebSocket
- Fix infinite re-render loop in configStore (pre-compute enabled
  cameras instead of deriving in selector)
- Fix mqtt_bridge global variable scope in broadcast()
- Add React ErrorBoundary for visible crash reporting
- Remove unused go2rtcUrl dependency from useStream hook

frontend/src/components/player/FullscreenView.tsx

@@ -5,7 +5,7 @@ import { CameraPlayer } from './CameraPlayer';
 
 export function FullscreenView() {
   const { fullscreenCamera, setFullscreenCamera } = useUIStore();
-  const cameras = useConfigStore((s) => s.enabledCameras());
+  const cameras = useConfigStore((s) => s.cameras);
 
   const currentIdx = cameras.findIndex((c) => c.name === fullscreenCamera);
   const camera = currentIdx >= 0 ? cameras[currentIdx] : null;