feat(message): implement incremental sync and atomic unread updates

Refactor the messaging system to improve synchronization efficiency and state consistency.

- Implement incremental message synchronization using sequence numbers (seq) to reduce payload size.
- Add `markAllAsRead` batch API support to optimize read receipt processing.
- Introduce atomic state updates in `useMessageStore` to prevent inconsistent UI rendering during unread count changes.
- Implement notification deduplication in `WSMessageHandler` to prevent duplicate unread increments during reconnection.
- Optimize `MessageSyncService` to prioritize incremental sync over full snapshots when local data exists.
- Refactor `ReadReceiptManager` to use optimistic updates with proper rollback mechanisms.
- Fix minor UI issues in `SettingsScreen` and `PrivacySettingsScreen` related to theme picker z-index and style application.

src/stores/message/store.ts

@@ -100,6 +100,14 @@ export interface MessageActions {
   setNotificationMuted: (conversationId: string, notificationMuted: boolean) => void;
   setInitialized: (initialized: boolean) => void;
 
+  // 原子性更新（避免中间渲染状态）
+  updateConversationWithUnread: (
+    conversation: ConversationResponse,
+    totalUnread: number,
+    systemUnread: number,
+  ) => void;
+  incrementUnreadAtomic: (conversationId: string) => void;
+
   // 重置
   reset: () => void;
 }
@@ -439,6 +447,53 @@ export const useMessageStore = create<MessageStore>((set, get) => ({
     set({ isInitialized: initialized });
   },
 
+  updateConversationWithUnread: (
+    conversation: ConversationResponse,
+    totalUnread: number,
+    systemUnread: number,
+  ) => {
+    const id = normalizeConversationId(conversation.id);
+    set(state => {
+      const newConversations = new Map(state.conversations);
+      newConversations.set(id, { ...conversation, id });
+      const conversationList = sortConversationList(newConversations);
+      const newNotificationMutedMap = new Map(state.notificationMutedMap);
+      if (conversation.notification_muted) {
+        newNotificationMutedMap.set(id, true);
+      } else {
+        newNotificationMutedMap.delete(id);
+      }
+      return {
+        conversations: newConversations,
+        conversationList,
+        notificationMutedMap: newNotificationMutedMap,
+        totalUnreadCount: totalUnread,
+        systemUnreadCount: systemUnread,
+      };
+    });
+  },
+
+  incrementUnreadAtomic: (conversationId: string) => {
+    const normalizedId = normalizeConversationId(conversationId);
+    set(state => {
+      const conversation = state.conversations.get(normalizedId);
+      if (!conversation) return state;
+
+      const newConversations = new Map(state.conversations);
+      newConversations.set(normalizedId, {
+        ...conversation,
+        unread_count: (conversation.unread_count || 0) + 1,
+      });
+      const conversationList = sortConversationList(newConversations);
+
+      return {
+        conversations: newConversations,
+        conversationList,
+        totalUnreadCount: state.totalUnreadCount + 1,
+      };
+    });
+  },
+
   // ==================== 重置 ====================
 
   reset: () => {