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/dependencies.py

@@ -24,6 +24,7 @@ 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.automations.automation_engine import AutomationEngine
 from wled_controller.core.weather.weather_manager import WeatherManager
 from wled_controller.core.backup.auto_backup import AutoBackupEngine
@@ -131,6 +132,10 @@ def get_weather_manager() -> WeatherManager:
     return _get("weather_manager", "Weather manager")
 
 
+def get_asset_store() -> AssetStore:
+    return _get("asset_store", "Asset store")
+
+
 def get_database() -> Database:
     return _get("database", "Database")
 
@@ -187,6 +192,7 @@ def init_dependencies(
     weather_source_store: WeatherSourceStore | None = None,
     weather_manager: WeatherManager | None = None,
     update_service: UpdateService | None = None,
+    asset_store: AssetStore | None = None,
 ):
     """Initialize global dependencies."""
     _deps.update({
@@ -213,4 +219,5 @@ def init_dependencies(
         "weather_source_store": weather_source_store,
         "weather_manager": weather_manager,
         "update_service": update_service,
+        "asset_store": asset_store,
     })