feat(mobile): add huddles with LiveKit

Mirrors the desktop huddle window: tap the headphones button on a stream
to fetch a LiveKit token from Orion and join a video room. Active huddles
show a red badge on the stream card (participant count) and a red Join
pill in the stream top bar — both driven by huddle_active_participants
synced from the LiveKit webhook.

The HuddleScreen lives at its own route (not a modal/window): video tile
grid with placeholders for camera-off, mic/camera toggles, and a leave
button. Adds the LiveKit RN SDK plus the WebRTC + LiveKit Expo config
plugins for prebuild.

https://claude.ai/code/session_01Po5tAD17MXhnqGQ9hKh6PC

js/mobile/package.json

@@ -30,6 +30,11 @@
     "expo-status-bar": "~3.0.9",
     "expo-video": "~3.0.10",
     "firebase": "^12.10.0",
+    "@config-plugins/react-native-webrtc": "^12.0.0",
+    "@livekit/react-native": "^2.7.5",
+    "@livekit/react-native-expo-plugin": "^1.0.2",
+    "@livekit/react-native-webrtc": "^144.1.0",
+    "livekit-client": "^2.15.2",
     "lucide-react-native": "^0.575.0",
     "nativewind": "^4.1.23",
     "react": "19.1.0",