Improve stream reliability with stall detection and buffer management

Add video stall detection that monitors currentTime and auto-reconnects
after 15s of frozen video. Add MSE SourceBuffer trimming to prevent
QuotaExceededError from killing streams silently. Handle appendBuffer
errors with safe wrapper and SourceBuffer error listener. Wait for ICE
gathering before sending WebRTC offers. Add go2rtc stream availability
endpoint. Improve backend proxy error logging.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/routes/go2rtc_proxy.py

@@ -11,6 +11,20 @@ logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/api/go2rtc")
 
 
+@router.get("/streams")
+async def get_streams():
+    """Fetch available streams from go2rtc."""
+    config = get_config()
+    target = f"{config.go2rtc.url}/api/streams"
+    try:
+        async with httpx.AsyncClient() as client:
+            resp = await client.get(target, timeout=5.0)
+        return resp.json()
+    except Exception:
+        logger.error("Failed to fetch go2rtc streams from %s", target)
+        return {}
+
+
 @router.post("/webrtc")
 async def proxy_webrtc(request: Request, src: str):
     """Proxy WebRTC SDP exchange to go2rtc."""
@@ -66,5 +80,11 @@ async def proxy_mse_ws(ws: WebSocket, src: str):
                 forward_to_client(),
                 forward_to_upstream(),
             )
-    except (WebSocketDisconnect, websockets.ConnectionClosed, Exception):
-        pass
+    except WebSocketDisconnect:
+        logger.debug("Client disconnected from MSE proxy for %s", src)
+    except websockets.ConnectionClosed:
+        logger.debug("Upstream go2rtc closed for %s", src)
+    except ConnectionRefusedError:
+        logger.error("Cannot reach go2rtc at %s for stream %s", target, src)
+    except Exception:
+        logger.exception("MSE proxy error for stream %s", src)