Clean backend debug logging and standardize error reporting.

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

internal/pkg/websocket/websocket.go

@@ -293,7 +293,6 @@ func (m *WebSocketManager) IsUserOnline(userID string) bool {
 	m.mutex.RLock()
 	defer m.mutex.RUnlock()
 	_, ok := m.clients[userID]
-	log.Printf("[DEBUG IsUserOnline] 检查用户 %s, 结果=%v, 当前在线用户=%v", userID, ok, m.clients)
 	return ok
 }
 
@@ -305,9 +304,6 @@ func (m *WebSocketManager) sendMessage(broadcast *BroadcastMessage) {
 		return
 	}
 
-	log.Printf("[DEBUG WebSocket] sendMessage: 目标用户=%s, 当前在线用户数=%d, 消息类型=%s",
-		broadcast.TargetUser, len(m.clients), broadcast.Message.Type)
-
 	m.mutex.RLock()
 	defer m.mutex.RUnlock()
 
@@ -324,7 +320,6 @@ func (m *WebSocketManager) sendMessage(broadcast *BroadcastMessage) {
 
 		select {
 		case client.Send <- msgBytes:
-			log.Printf("[DEBUG WebSocket] 成功发送消息到用户 %s, 消息类型=%s", userID, broadcast.Message.Type)
 		default:
 			log.Printf("Failed to send message to user %s: channel full", userID)
 		}