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/message_repo.go

@@ -2,7 +2,6 @@ package repository
 
 import (
 	"carrot_bbs/internal/model"
-	"fmt"
 	"time"
 
 	"gorm.io/gorm"
@@ -40,8 +39,6 @@ func (r *MessageRepository) GetConversation(id string) (*model.Conversation, err
 func (r *MessageRepository) GetOrCreatePrivateConversation(user1ID, user2ID string) (*model.Conversation, error) {
 	var conv model.Conversation
 
-	fmt.Printf("[DEBUG] GetOrCreatePrivateConversation: user1ID=%s, user2ID=%s\n", user1ID, user2ID)
-
 	// 查找两个用户共同参与的私聊会话
 	err := r.db.Table("conversations c").
 		Joins("INNER JOIN conversation_participants cp1 ON c.id = cp1.conversation_id AND cp1.user_id = ?", user1ID).
@@ -53,7 +50,6 @@ func (r *MessageRepository) GetOrCreatePrivateConversation(user1ID, user2ID stri
 		_ = r.db.Model(&model.ConversationParticipant{}).
 			Where("conversation_id = ? AND user_id IN ?", conv.ID, []string{user1ID, user2ID}).
 			Update("hidden_at", nil).Error
-		fmt.Printf("[DEBUG] GetOrCreatePrivateConversation: found existing conversation, ID=%s\n", conv.ID)
 		return &conv, nil
 	}
 
@@ -62,7 +58,6 @@ func (r *MessageRepository) GetOrCreatePrivateConversation(user1ID, user2ID stri
 	}
 
 	// 没找到会话，创建新会话
-	fmt.Printf("[DEBUG] GetOrCreatePrivateConversation: no existing conversation found, creating new one\n")
 	conv = model.Conversation{
 		Type: model.ConversationTypePrivate,
 	}
@@ -85,10 +80,6 @@ func (r *MessageRepository) GetOrCreatePrivateConversation(user1ID, user2ID stri
 		return nil
 	})
 
-	if err == nil {
-		fmt.Printf("[DEBUG] GetOrCreatePrivateConversation: created new conversation, ID=%s\n", conv.ID)
-	}
-
 	return &conv, err
 }
 
@@ -153,20 +144,10 @@ func (r *MessageRepository) GetMessagesAfterSeq(conversationID string, afterSeq
 // GetMessagesBeforeSeq 获取指定seq之前的历史消息（用于下拉加载更多）
 func (r *MessageRepository) GetMessagesBeforeSeq(conversationID string, beforeSeq int64, limit int) ([]*model.Message, error) {
 	var messages []*model.Message
-	fmt.Printf("[DEBUG] GetMessagesBeforeSeq: conversationID=%s, beforeSeq=%d, limit=%d\n", conversationID, beforeSeq, limit)
 	err := r.db.Where("conversation_id = ? AND seq < ?", conversationID, beforeSeq).
 		Order("seq DESC"). // 降序获取最新消息在前
 		Limit(limit).
 		Find(&messages).Error
-	fmt.Printf("[DEBUG] GetMessagesBeforeSeq: found %d messages, seq range: ", len(messages))
-	for i, m := range messages {
-		if i < 5 || i >= len(messages)-2 {
-			fmt.Printf("%d ", m.Seq)
-		} else if i == 5 {
-			fmt.Printf("... ")
-		}
-	}
-	fmt.Println()
 	// 反转回正序
 	for i, j := 0, len(messages)-1; i < j; i, j = i+1, j-1 {
 		messages[i], messages[j] = messages[j], messages[i]