refactor: 自定义业务错误 (#33)

* refactor: 自定义业务错误

* refactor: 隐藏服务器错误与统一 panic 响应

backend/cmd/server/main.go

@@ -84,7 +84,7 @@ func main() {
 
 func runSetupServer() {
 	r := gin.New()
-	r.Use(gin.Recovery())
+	r.Use(middleware.Recovery())
 	r.Use(middleware.CORS())
 
 	// Register setup routes