feat(message): enhance message store management and UI stability

Implement `removeMessage` in `useMessageStore` to allow for atomic message deletion from the state. Improve `useChatScreen` loading logic to prevent layout jumps and ensure consistent UI state during initial message loading. Additionally, add type safety for WebSocket sequence numbers and optimize message selector stability.

- Add `removeMessage` action to `useMessageStore` for state-consistent deletions
- Refine `useChatScreen` loading state logic to prevent FlashList layout issues
- Ensure `useMessages` hook returns a stable `EMPTY_MESSAGES` constant
- Cast WebSocket `seq` to integer to ensure consistent numeric comparison
- Update `useChatScreen` to use `useMessageStore` for immediate local deletion feedback

src/stores/message/hooks.ts

@@ -18,6 +18,8 @@ import { messageManager } from './MessageManager';
 import { useMessageStore } from './store';
 import { useUnreadCountQuery } from '../../hooks/useUnreadCount';
 
+const EMPTY_MESSAGES: MessageResponse[] = [];
+
 // ==================== useConversations - 获取会话列表 ====================
 
 interface UseConversationsReturn {
@@ -100,9 +102,10 @@ export function useMessages(conversationId: string | null): UseMessagesReturn {
   
   // 使用 useShallow 避免每次返回新数组引用导致的无限循环
   const messages = useMessageStore(
-    useShallow(state => 
-      normalizedConversationId ? (state.messagesMap.get(normalizedConversationId) || []) : []
-    )
+    useShallow(state => {
+      if (!normalizedConversationId) return EMPTY_MESSAGES;
+      return state.messagesMap.get(normalizedConversationId) ?? EMPTY_MESSAGES;
+    })
   );
   const isLoadingMessages = useMessageStore(state => 
     normalizedConversationId ? state.loadingMessagesSet.has(normalizedConversationId) : false