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/config.py

@@ -15,7 +15,7 @@ class ServerConfig(BaseSettings):
     host: str = "0.0.0.0"
     port: int = 8080
     log_level: str = "INFO"
-    cors_origins: List[str] = ["*"]
+    cors_origins: List[str] = ["http://localhost:8080"]
 
 
 class AuthConfig(BaseSettings):
@@ -24,6 +24,13 @@ class AuthConfig(BaseSettings):
     api_keys: dict[str, str] = {}  # label: key mapping (empty = auth disabled)
 
 
+class AssetsConfig(BaseSettings):
+    """Assets configuration."""
+
+    max_file_size_mb: int = 50          # Max upload size in MB
+    assets_dir: str = "data/assets"     # Directory for uploaded asset files
+
+
 class StorageConfig(BaseSettings):
     """Storage configuration."""
 
@@ -65,16 +72,21 @@ class Config(BaseSettings):
     server: ServerConfig = Field(default_factory=ServerConfig)
     auth: AuthConfig = Field(default_factory=AuthConfig)
     storage: StorageConfig = Field(default_factory=StorageConfig)
+    assets: AssetsConfig = Field(default_factory=AssetsConfig)
     mqtt: MQTTConfig = Field(default_factory=MQTTConfig)
     logging: LoggingConfig = Field(default_factory=LoggingConfig)
 
     def model_post_init(self, __context: object) -> None:
-        """Override storage paths when demo mode is active."""
+        """Override storage and assets paths when demo mode is active."""
         if self.demo:
-            for field_name in self.storage.model_fields:
+            for field_name in StorageConfig.model_fields:
                 value = getattr(self.storage, field_name)
                 if isinstance(value, str) and value.startswith("data/"):
                     setattr(self.storage, field_name, value.replace("data/", "data/demo/", 1))
+            for field_name in AssetsConfig.model_fields:
+                value = getattr(self.assets, field_name)
+                if isinstance(value, str) and value.startswith("data/"):
+                    setattr(self.assets, field_name, value.replace("data/", "data/demo/", 1))
 
     @classmethod
     def from_yaml(cls, config_path: str | Path) -> "Config":