Centralize configuration into config.yaml

- All settings moved to config.yaml
- configs/load.py reads from config.yaml with env var overrides
- Environment variables still work for backward compatibility
- Added pyyaml to requirements

app/main.py

@@ -13,7 +13,11 @@ from app.core.lifecycle import startup
 from app.signaling.websocket_server import main as serve
 
 
-if __name__ == "__main__":
+def main():
     startup()
     logger.info("Starting server...")
     asyncio.run(serve())
+
+
+if __name__ == "__main__":
+    main()