feat: implement OpenAI-compatible Realtime API with authentication and management features

- Added support for public Realtime API, including new routes for managing API keys and handling WebRTC connections.
- Introduced RealtimeApiKey model and associated CRUD operations for admin management of API keys.
- Implemented authentication mechanisms for API keys and client secrets.
- Enhanced environment configuration with new secrets for Realtime API.
- Created OpenAIRealtime session management and event processing for real-time interactions.
- Updated schemas and settings to accommodate new features and ensure compatibility with existing systems.

backend/.env.example

@@ -14,6 +14,11 @@ PORT=8000
 # 前端开发地址,允许跨域(公网部署时加上实际前端 origin)
 CORS_ORIGINS=http://localhost:3000,http://127.0.0.1:3000
 
+# ---- OpenAI-compatible Realtime API ----
+# 用独立随机值签名长期 API Key 摘要和短期 Client Secret；生产环境必须修改。
+REALTIME_TOKEN_SECRET=replace-with-a-long-random-secret
+REALTIME_CLIENT_SECRET_TTL_SECONDS=60
+
 # ---- RustFS / S3-compatible storage ----
 # Use 127.0.0.1 (not localhost) if HTTP_PROXY is set — proxies often return 502 for localhost.
 S3_ENDPOINT_URL=http://127.0.0.1:9000