feat(processed-audio-sources): phase 1 - audio filter framework

Add the foundation for audio processing filters, mirroring the existing
picture filter/postprocessing template system:
- AudioFilter base class, AudioFilterRegistry, AudioFilterOptionDef
- AudioProcessingTemplate dataclass + SQLite-backed store
- audio_filter_template meta-filter with recursive resolution
- Full REST API: CRUD templates + filter registry discovery
- Dependency injection wired in dependencies.py and main.py

server/src/wled_controller/api/__init__.py

@@ -28,6 +28,8 @@ from .routes.assets import router as assets_router
 from .routes.home_assistant import router as home_assistant_router
 from .routes.mqtt import router as mqtt_router
 from .routes.game_integration import router as game_integration_router
+from .routes.audio_processing_templates import router as audio_processing_templates_router
+from .routes.audio_filters import router as audio_filters_router
 
 router = APIRouter()
 router.include_router(system_router)
@@ -56,5 +58,7 @@ router.include_router(assets_router)
 router.include_router(home_assistant_router)
 router.include_router(mqtt_router)
 router.include_router(game_integration_router)
+router.include_router(audio_processing_templates_router)
+router.include_router(audio_filters_router)
 
 __all__ = ["router"]