refactor: 架构重构 - 解耦过度耦合模块

主要改动:
1. 创建乐观更新工具函数 (optimisticUpdate.ts)
   - 消除 userStore.ts 中的重复代码

2. 拆分 useResponsive.ts (485行 -> 12个专注模块)
   - useBreakpoint: 断点检测
   - useOrientation: 方向检测
   - usePlatform: 平台检测
   - useScreenSize: 屏幕尺寸
   - useResponsiveValue: 响应式值
   - useResponsiveStyle: 响应式样式
   - useMediaQuery: 媒体查询
   - useColumnCount: 列数计算
   - useResponsiveSpacing: 响应式间距

3. 整理数据层 (Repository 层)
   - ApiDataSource: API数据源
   - LocalDataSource: 本地数据源
   - CacheDataSource: 缓存数据源
   - MessageRepository: 消息仓库

4. 重构 messageManager.ts (2194行 -> 4个模块)
   - MessageStateManager: 状态管理
   - WebSocketMessageHandler: WebSocket处理
   - MessageSyncService: 消息同步
   - ReadReceiptManager: 已读管理

5. 导航解耦 (MainNavigator.tsx: 1118行 -> 100行)
   - 创建 NavigationService 解耦层
   - 拆分多个 Navigator 组件

架构改进:
- 单一职责原则: 每个模块职责明确
- 依赖倒置: 通过接口解耦
- 代码复用: 工具函数可被多处使用
- 可测试性: 各模块可独立测试

src/data/mappers/PostMapper.ts

@@ -0,0 +1,123 @@
+/**
+ * 帖子数据映射器
+ * 负责 Post 模型与 API 响应之间的转换
+ */
+
+import { PostModel, UserModel } from '../models';
+import type { Post } from '../../types';
+
+export class PostMapper {
+  /**
+   * 将 API 响应转换为应用模型
+   */
+  static fromApiResponse(response: Post): PostModel {
+    return {
+      id: String(response.id || ''),
+      authorId: String(response.author_id || ''),
+      author: response.author ? this.mapAuthorFromApi(response.author) : undefined,
+      title: response.title || '',
+      content: response.content || '',
+      images: response.images || [],
+      likeCount: response.like_count || 0,
+      commentCount: response.comment_count || 0,
+      shareCount: response.share_count || 0,
+      viewCount: response.view_count || 0,
+      favoriteCount: response.favorite_count || 0,
+      isLiked: response.is_liked || false,
+      isFavorited: response.is_favorited || false,
+      isTop: response.is_top || false,
+      status: response.status || 'published',
+      communityId: response.community_id,
+      tags: response.tags || [],
+      createdAt: new Date(response.created_at || Date.now()),
+      updatedAt: new Date(response.updated_at || Date.now()),
+    };
+  }
+
+  /**
+   * 将 API 响应数组转换为应用模型数组
+   */
+  static fromApiResponseList(responses: Post[]): PostModel[] {
+    return responses.map(r => this.fromApiResponse(r));
+  }
+
+  /**
+   * 将应用模型转换为 API 请求数据
+   */
+  static toApiRequest(model: Partial<PostModel>): Record<string, any> {
+    const request: Record<string, any> = {};
+
+    if (model.title !== undefined) {
+      request.title = model.title;
+    }
+    if (model.content !== undefined) {
+      request.content = model.content;
+    }
+    if (model.images !== undefined) {
+      request.images = model.images;
+    }
+    if (model.communityId !== undefined) {
+      request.community_id = model.communityId;
+    }
+    if (model.tags !== undefined) {
+      request.tags = model.tags;
+    }
+
+    return request;
+  }
+
+  /**
+   * 创建帖子请求
+   */
+  static createPostRequest(
+    title: string,
+    content: string,
+    images?: string[],
+    communityId?: string
+  ): Record<string, any> {
+    const request: Record<string, any> = {
+      title,
+      content,
+    };
+    if (images && images.length > 0) {
+      request.images = images;
+    }
+    if (communityId) {
+      request.community_id = communityId;
+    }
+    return request;
+  }
+
+  /**
+   * 更新帖子请求
+   */
+  static updatePostRequest(
+    title?: string,
+    content?: string,
+    images?: string[]
+  ): Record<string, any> {
+    const request: Record<string, any> = {};
+    if (title !== undefined) {
+      request.title = title;
+    }
+    if (content !== undefined) {
+      request.content = content;
+    }
+    if (images !== undefined) {
+      request.images = images;
+    }
+    return request;
+  }
+
+  /**
+   * 映射作者信息
+   */
+  private static mapAuthorFromApi(author: any): UserModel {
+    return {
+      id: String(author.id || ''),
+      username: author.username || '',
+      nickname: author.nickname,
+      avatar: author.avatar,
+    };
+  }
+}