feat: 完善模型管理功能

- 新增模型 API 路由，支持 CRUD 和测试连接
- 支持 MiniMax、GLM、OpenAI Compatible 三种供应商
- 添加连接状态持久化 (untested/connected/disconnected)
- 修复 CORS 和数据库模型兼容性问题
- 前端 UI 优化：供应商默认 API 地址自动填充

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/api/v1/__init__.py

@@ -4,7 +4,7 @@ API v1 Router
 
 from fastapi import APIRouter
 
-from app.api.v1 import files, projects, chunks, questions, datasets, eval
+from app.api.v1 import files, projects, chunks, questions, datasets, eval, models
 
 api_router = APIRouter()
 
@@ -15,3 +15,4 @@ api_router.include_router(chunks.router, prefix="/chunks", tags=["chunks"])
 api_router.include_router(questions.router, prefix="/questions", tags=["questions"])
 api_router.include_router(datasets.router, prefix="/datasets", tags=["datasets"])
 api_router.include_router(eval.router, prefix="/eval", tags=["eval"])
+api_router.include_router(models.router, prefix="/models", tags=["models"])