fix: 更新后端服务

- main.go: 更新模型初始化
- agent_repo, model_service: 优化

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

server/internal/service/model_service.go

@@ -137,15 +137,15 @@ func (s *ModelService) TestConnection(req model.TestModelRequest) (*model.TestMo
 			// chat 模型使用 /chat/completions
 			switch req.Provider {
 			case "OpenAI":
-				baseURL = baseURL + "/v1/chat/completions"
+				baseURL = baseURL + "/chat/completions"
 			case "Ollama":
 				baseURL = baseURL + "/api/chat"
 			case "ali", "Ali", "aliyun", "Aliyun":
 				// 阿里云 DashScope 兼容 OpenAI 格式
 				baseURL = baseURL + "/chat/completions"
 			default:
-				// 默认使用 OpenAI 兼容格式
-				baseURL = baseURL + "/v1/chat/completions"
+				// 默认使用 /chat/completions
+				baseURL = baseURL + "/chat/completions"
 			}
 		}
 	}