Refactor backend configuration management and update environment settings

- Replace the `config.py` module with a new `settings.py` to streamline environment variable management, focusing on database, CORS, and TURN settings.
- Update references throughout the backend codebase to use the new `settings` module instead of the deprecated `config`.
- Modify the `.env.example` file to reflect the new configuration approach, indicating that model provider credentials should be maintained separately.
- Enhance the `AssistantConfig` model to clarify the source of runtime connection information, ensuring it is injected from model resources rather than relying on defaults from the environment.
- Introduce new user scripts for audio and video management in the Tampermonkey environment, enhancing WebRTC capabilities.

backend/app.py

@@ -14,7 +14,7 @@
 
 from contextlib import asynccontextmanager
 
-import config
+import settings
 import uvicorn
 from db.session import sync_interface_definitions
 from fastapi import FastAPI
@@ -41,7 +41,7 @@ app = FastAPI(title="AI Video Assistant 平台 - 后端", lifespan=lifespan)
 
 app.add_middleware(
     CORSMiddleware,
-    allow_origins=config.CORS_ORIGINS,
+    allow_origins=settings.CORS_ORIGINS,
     allow_credentials=True,
     allow_methods=["*"],
     allow_headers=["*"],
@@ -57,4 +57,4 @@ app.include_router(voice_ws.router)
 
 
 if __name__ == "__main__":
-    uvicorn.run("app:app", host=config.HOST, port=config.PORT, reload=True)
+    uvicorn.run("app:app", host=settings.HOST, port=settings.PORT, reload=True)