refactor(Post, PostMapper, PostRepository, CreatePostScreen, HomeScreen): update communityId to channelId for improved clarity

- Renamed communityId to channelId across Post entity, PostMapper, and PostRepository for consistency and clarity.
- Updated CreatePostScreen to include channel selection functionality, enhancing user experience when creating posts.
- Adjusted HomeScreen to support filtering posts by channel, improving content organization.
- Refactored related interfaces and services to align with the new channelId terminology, ensuring a cohesive codebase.

src/infrastructure/diff/postTypes.ts

@@ -113,7 +113,7 @@ export interface BasePostUpdate {
   /** 更新时间戳 */
   timestamp: number;
   /** 社区 ID（可选） */
-  communityId?: string;
+  channelId?: string;
   /** 载荷数据（可选，用于合并更新） */
   payload?: Record<string, any>;
 }