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/services/model_resource_tester.py

@@ -12,10 +12,10 @@ from urllib.parse import parse_qsl, urlencode, urlsplit, urlunsplit
 import httpx
 from websockets.asyncio.client import connect as websocket_connect
 
-import config
 from schemas import ModelResourceTestResult
 
 TEST_TIMEOUT_SECONDS = 10.0
+DEFAULT_TEST_TTS_VOICE = "alloy"
 
 
 def _endpoint(base_url: str, path: str) -> str:
@@ -116,7 +116,7 @@ async def test_model_resource(
                     json={
                         "model": model_id,
                         "input": "测试",
-                        "voice": str(values.get("voice") or config.TTS_VOICE),
+                        "voice": str(values.get("voice") or DEFAULT_TEST_TTS_VOICE),
                         "response_format": "pcm",
                         "speed": float(values.get("speed") or 1),
                     },