refactor(post): consolidate post sync to PostSyncService and remove ProcessPostUseCase

- Replace ProcessPostUseCase with new PostSyncService in src/services/post/
- Add postListStore for state management in src/stores/post/
- Remove deprecated ProcessPostUseCase and ProcessMessageUseCase files
- Delete architecture documentation files (ARCHITECTURE_REFACTOR_PLAN.md, architecture-comparison-report.md)
- Update all consumers (HomeScreen, PostDetailScreen, SearchScreen, useUserProfile, useDifferentialPosts)
- Simplify postService to only contain API layer methods
- Remove unused type exports from message stores

BREAKING CHANGE: ProcessPostUseCase and ProcessMessageUseCase have been removed.
Use postSyncService for post operations instead.

src/stores/message/index.ts

@@ -23,15 +23,10 @@ export type { MessageState, MessageActions, MessageStore } from './store';
 // ==================== 类型导出 ====================
 // 从 types.ts 导出所有类型
 export type {
-  MessageEventType,
-  MessageEvent,
-  MessageSubscriber,
   MessageManagerState,
   ReadStateRecord,
   MessageManagerConversationListDeps,
   HandleNewMessageOptions,
-  // 服务接口类型（保留向后兼容，但服务层已不再使用）
-  IMessageStateManager,
   IMessageDeduplication,
   IUserCacheService,
   IReadReceiptManager,