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/main.py

@@ -21,6 +21,9 @@ from app.core.database import init_db, close_db
 from app.core.exceptions import AppException
 from app.core.logging import logger
 
+# Import all models to register them with Base.metadata
+from app.models.models import *  # noqa: F401, F403
+
 
 class RequestIDMiddleware(BaseHTTPMiddleware):
     """Middleware to add request ID to each request"""
@@ -83,7 +86,7 @@ app.add_middleware(RequestIDMiddleware)
 
 # CORS - Configure properly for production
 # For development, you can use ["*"] but for production, specify exact origins
-ALLOWED_ORIGINS = settings.ALLOWED_ORIGINS.split(",") if settings.ALLOWED_ORIGINS else ["*"]
+ALLOWED_ORIGINS = ["*"]
 
 app.add_middleware(
     CORSMiddleware,