refactor(message): implement atomic message merging and patching to prevent race conditions

Introduce `mergeMessages` and `patchMessages` to the message store to handle
updates atomically within Zustand's `set` callback. This replaces manual
read-modify-write patterns in services, preventing message loss during
concurrent WebSocket updates and synchronization processes.

- Add `mergeMessages` for atomic merging of new messages into existing lists
- Add `patchMessages` for efficient field updates (e.g., sender info, status)
- Update `MessageSendService`, `MessageSyncService`, and `WSMessageHandler`
  to use these new atomic operations
- Remove reliance on external `mergeMessagesById` in service layers to
  ensure state consistency

src/stores/message/services/MessageSendService.ts

@@ -7,7 +7,7 @@ import type { MessageResponse, MessageSegment, ConversationResponse } from '../.
 import { messageService } from '@/services/message';
 import { messageRepository } from '@/database';
 import type { IMessageSendService } from '../types';
-import { useMessageStore, mergeMessagesById } from '../store';
+import { useMessageStore } from '../store';
 
 export class MessageSendService implements IMessageSendService {
   private getCurrentUserId: () => string | null;
@@ -36,8 +36,7 @@ export class MessageSendService implements IMessageSendService {
       if (response) {
         const currentUserId = this.getCurrentUserId();
         
-        // 添加到本地消息列表
-        const existingMessages = store.getMessages(conversationId);
+        // 原子性合并新消息到内存（防止并发 WS 消息丢失）
         const newMessage: MessageResponse = {
           id: response.id,
           conversation_id: conversationId,
@@ -48,8 +47,7 @@ export class MessageSendService implements IMessageSendService {
           status: 'normal',
         };
 
-        const updatedMessages = mergeMessagesById(existingMessages, [newMessage]);
-        store.setMessages(conversationId, updatedMessages);
+        store.mergeMessages(conversationId, [newMessage]);
 
         // 更新会话最后消息
         this.updateConversationWithNewMessage(conversationId, newMessage);