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/helpers.go

@@ -62,6 +62,19 @@ func UserToUserInfo(user *model.User) *types.UserInfo {
 	}
 }
 
+// UserToPublicUserInfo 将 User 模型转换为 PublicUserInfo 响应
+func UserToPublicUserInfo(user *model.User) *types.PublicUserInfo {
+	return &types.PublicUserInfo{
+		ID:        user.ID,
+		Username:  user.Username,
+		Avatar:    user.Avatar,
+		Points:    user.Points,
+		Role:      user.Role,
+		Status:    user.Status,
+		CreatedAt: user.CreatedAt,
+	}
+}
+
 // ProfileToProfileInfo 将 Profile 模型转换为 ProfileInfo 响应
 func ProfileToProfileInfo(profile *model.Profile) *types.ProfileInfo {
 	return &types.ProfileInfo{