Clean backend debug logging and standardize error reporting.

This removes verbose trace output in handlers/services and keeps only actionable error-level logs.

internal/handler/user_handler.go

@@ -1,7 +1,6 @@
 package handler
 
 import (
-	"fmt"
 	"strconv"
 
 	"github.com/gin-gonic/gin"
@@ -572,16 +571,12 @@ func (h *UserHandler) GetFollowersList(c *gin.Context) {
 	page := c.DefaultQuery("page", "1")
 	pageSize := c.DefaultQuery("page_size", "20")
 
-	fmt.Printf("[DEBUG] GetFollowersList: userID=%s, currentUserID=%s\n", userID, currentUserID)
-
 	users, err := h.userService.GetFollowersList(c.Request.Context(), userID, page, pageSize)
 	if err != nil {
 		response.InternalServerError(c, "failed to get followers list")
 		return
 	}
 
-	fmt.Printf("[DEBUG] GetFollowersList: found %d users\n", len(users))
-
 	// 如果已登录，获取双向关注状态和实时计算的帖子数量
 	var userResponses []*dto.UserResponse
 	if currentUserID != "" && len(users) > 0 {
@@ -589,7 +584,6 @@ func (h *UserHandler) GetFollowersList(c *gin.Context) {
 		for i, u := range users {
 			userIDs[i] = u.ID
 		}
-		fmt.Printf("[DEBUG] GetFollowersList: checking mutual follow status for userIDs=%v\n", userIDs)
 		statusMap, _ := h.userService.GetMutualFollowStatus(c.Request.Context(), currentUserID, userIDs)
 		postsCountMap, _ := h.userService.GetUserPostCountBatch(c.Request.Context(), userIDs)
 		userResponses = dto.ConvertUsersToResponseWithMutualFollowAndPostsCount(users, statusMap, postsCountMap)