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/message_handler.go

@@ -2,7 +2,6 @@ package handler
 
 import (
 	"context"
-	"fmt"
 	"strconv"
 
 	"github.com/gin-gonic/gin"
@@ -145,14 +144,11 @@ func (h *MessageHandler) GetConversationByID(c *gin.Context) {
 	}
 
 	conversationIDStr := c.Param("id")
-	fmt.Printf("[DEBUG] GetConversationByID: conversationIDStr = %s\n", conversationIDStr)
 	conversationID, err := service.ParseConversationID(conversationIDStr)
 	if err != nil {
-		fmt.Printf("[DEBUG] GetConversationByID: failed to parse conversation ID: %v\n", err)
 		response.BadRequest(c, "invalid conversation id")
 		return
 	}
-	fmt.Printf("[DEBUG] GetConversationByID: conversationID = %s\n", conversationID)
 
 	conv, err := h.chatService.GetConversationByID(c.Request.Context(), conversationID, userID)
 	if err != nil {
@@ -281,14 +277,11 @@ func (h *MessageHandler) SendMessage(c *gin.Context) {
 	}
 
 	conversationIDStr := c.Param("id")
-	fmt.Printf("[DEBUG] SendMessage: conversationIDStr = %s\n", conversationIDStr)
 	conversationID, err := service.ParseConversationID(conversationIDStr)
 	if err != nil {
-		fmt.Printf("[DEBUG] SendMessage: failed to parse conversation ID: %v\n", err)
 		response.BadRequest(c, "invalid conversation id")
 		return
 	}
-	fmt.Printf("[DEBUG] SendMessage: conversationID = %s, userID = %s\n", conversationID, userID)
 
 	var req dto.SendMessageRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
@@ -507,11 +500,8 @@ func (h *MessageHandler) MarkAsRead(c *gin.Context) {
 // GET /api/conversations/unread/count
 func (h *MessageHandler) GetUnreadCount(c *gin.Context) {
 	userID := c.GetString("user_id")
-	// 添加调试日志
-	fmt.Printf("[DEBUG] GetUnreadCount: user_id from context = %q\n", userID)
 
 	if userID == "" {
-		fmt.Printf("[DEBUG] GetUnreadCount: user_id is empty, returning 401\n")
 		response.Unauthorized(c, "")
 		return
 	}