feat: Add public user information retrieval endpoint

- Introduced a new endpoint to fetch public user information without authentication.
- Implemented UserToPublicUserInfo function to format user data for the response.
- Updated UserService interface and user service implementation to support fetching users by username.
- Enhanced user handler to validate input parameters and check user status before responding.

internal/handler/routes.go

@@ -93,6 +93,10 @@ func registerAuthRoutes(v1 *gin.RouterGroup, h *AuthHandler) {
 
 // registerUserRoutes 注册用户路由
 func registerUserRoutes(v1 *gin.RouterGroup, h *UserHandler, jwtService *auth.JWTService) {
+	// 公开用户信息路由（无需认证）
+	v1.GET("/users/public", h.GetPublicInfo)
+
+	// 需要认证的用户路由
 	userGroup := v1.Group("/user")
 	userGroup.Use(middleware.AuthMiddleware(jwtService))
 	{