feat: asset-based image/video sources, notification sounds, UI improvements

- Replace URL-based image_source/url fields with image_asset_id/video_asset_id
  on StaticImagePictureSource and VideoCaptureSource (clean break, no migration)
- Resolve asset IDs to file paths at runtime via AssetStore.get_file_path()
- Add EntitySelect asset pickers for image/video in stream editor modal
- Add notification sound configuration (global sound + per-app overrides)
- Unify per-app color and sound overrides into single "Per-App Overrides" section
- Persist notification history between server restarts
- Add asset management system (upload, edit, delete, soft-delete)
- Replace emoji buttons with SVG icons throughout UI
- Various backend improvements: SQLite stores, auth, backup, MQTT, webhooks

server/src/wled_controller/api/routes/value_sources.py

@@ -245,6 +245,7 @@ async def test_value_source_ws(
             await websocket.send_json({"value": round(value, 4)})
             await asyncio.sleep(0.05)
     except WebSocketDisconnect:
+        logger.debug("Value source test WebSocket disconnected for %s", source_id)
         pass
     except Exception as e:
         logger.error(f"Value source test WebSocket error for {source_id}: {e}")