Clean backend debug logging and standardize error reporting.

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

internal/repository/user_repo.go

@@ -2,7 +2,6 @@ package repository
 
 import (
 	"carrot_bbs/internal/model"
-	"fmt"
 
 	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
@@ -362,8 +361,6 @@ func (r *UserRepository) GetMutualFollowStatus(currentUserID string, targetUserI
 		return result, nil
 	}
 
-	fmt.Printf("[DEBUG] GetMutualFollowStatus: currentUserID=%s, targetUserIDs=%v\n", currentUserID, targetUserIDs)
-
 	// 初始化所有目标用户为未关注状态
 	for _, userID := range targetUserIDs {
 		result[userID] = [2]bool{false, false}
@@ -377,7 +374,6 @@ func (r *UserRepository) GetMutualFollowStatus(currentUserID string, targetUserI
 	if err != nil {
 		return nil, err
 	}
-	fmt.Printf("[DEBUG] GetMutualFollowStatus: currentUser follows these targets: %v\n", followingIDs)
 	for _, id := range followingIDs {
 		status := result[id]
 		status[0] = true
@@ -392,13 +388,11 @@ func (r *UserRepository) GetMutualFollowStatus(currentUserID string, targetUserI
 	if err != nil {
 		return nil, err
 	}
-	fmt.Printf("[DEBUG] GetMutualFollowStatus: these targets follow currentUser: %v\n", followerIDs)
 	for _, id := range followerIDs {
 		status := result[id]
 		status[1] = true
 		result[id] = status
 	}
 
-	fmt.Printf("[DEBUG] GetMutualFollowStatus: final result=%v\n", result)
 	return result, nil
 }