Refactor backend to support interface-definition driven model resources

- Introduce a new model structure for managing interface definitions and model resources, enhancing the backend's capability to handle various service integrations.
- Update the Makefile to reflect changes in database seeding and resource management commands.
- Remove the deprecated credentials management routes and replace them with a unified model registry API.
- Modify existing routes and schemas to align with the new model structure, ensuring seamless integration with the frontend.
- Enhance database seeding scripts to populate new model resources and their configurations.
- Update README documentation to reflect the new architecture and usage instructions for model resources and interface definitions.

deploy/README.md

@@ -9,7 +9,7 @@
 ```
 浏览器 ──https/wss──> nginx :443 (唯一 TLS 入口, mkcert 证书)
                        ├── /ws/    → 后端 :8000  (/ws/voice 信令、/ws/stream 裸流)
-                       ├── /api/   → 后端 :8000  (assistants/credentials/...)
+                       ├── /api/   → 后端 :8000  (assistants/model-resources/...)
                        ├── /health → 后端 :8000
                        └── /       → 前端 :3000  (Next dev + HMR)
 ```

deploy/nginx/ai-video.dev.conf

@@ -62,7 +62,7 @@ http {
             proxy_buffering off;            # 流式音频不能攒着
         }
 
-        # ---- 后端 HTTP 接口:/api/*(assistants/credentials/knowledge-bases)+ /health ----
+        # ---- 后端 HTTP 接口:/api/*(assistants/model-resources/knowledge-bases)+ /health ----
         location /api/ {
             proxy_pass http://127.0.0.1:8000;
             proxy_http_version 1.1;