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/main.py

@@ -34,6 +34,7 @@ from wled_controller.storage.sync_clock_store import SyncClockStore
 from wled_controller.storage.color_strip_processing_template_store import ColorStripProcessingTemplateStore
 from wled_controller.storage.gradient_store import GradientStore
 from wled_controller.storage.weather_source_store import WeatherSourceStore
+from wled_controller.storage.asset_store import AssetStore
 from wled_controller.core.processing.sync_clock_manager import SyncClockManager
 from wled_controller.core.weather.weather_manager import WeatherManager
 from wled_controller.core.automations.automation_engine import AutomationEngine
@@ -80,6 +81,12 @@ cspt_store = ColorStripProcessingTemplateStore(db)
 gradient_store = GradientStore(db)
 gradient_store.migrate_palette_references(color_strip_store)
 weather_source_store = WeatherSourceStore(db)
+asset_store = AssetStore(db, config.assets.assets_dir)
+
+# Import prebuilt notification sounds on first run
+_prebuilt_sounds_dir = Path(__file__).parent / "data" / "prebuilt_sounds"
+asset_store.import_prebuilt_sounds(_prebuilt_sounds_dir)
+
 sync_clock_manager = SyncClockManager(sync_clock_store)
 weather_manager = WeatherManager(weather_source_store)
 
@@ -98,6 +105,7 @@ processor_manager = ProcessorManager(
         cspt_store=cspt_store,
         gradient_store=gradient_store,
         weather_manager=weather_manager,
+        asset_store=asset_store,
     )
 )
 
@@ -190,6 +198,7 @@ async def lifespan(app: FastAPI):
         weather_source_store=weather_source_store,
         weather_manager=weather_manager,
         update_service=update_service,
+        asset_store=asset_store,
     )
 
     # Register devices in processor manager for health monitoring