refactor(database): migrate to new modular database layer and unify data access

- Remove legacy database.ts, LocalDataSource.ts, and MessageRepository.ts
- Create new src/database/ module with messageRepository, userCacheRepository, conversationRepository, and groupCacheRepository
- Update all consumers to import from @/database instead of services/database
- Add web platform blur handling for modal components to fix focus issues
- Flatten SystemMessageItem and NotificationsScreen styles for consistent design
- Add draggable slider in ChatSettingsScreen and dynamic font size support
- Introduce 9 new chat color themes
- Add profile screens for about, terms, and privacy policy with navigation routes
- Add policy links to login and registration screens
- Fix post share URL format from /posts/ to /post/

src/data/datasources/interfaces.ts

@@ -20,6 +20,8 @@ export interface ILocalDataSource {
   run(sql: string, params?: any[]): Promise<{ lastInsertRowId: number; changes: number }>;
   transaction(operations: () => Promise<void>): Promise<void>;
   batch(operations: (db: ILocalDataSource) => Promise<void>): Promise<void>;
+  enqueueWrite<T>(operation: () => Promise<T>): Promise<T>;
+  initialize(userId?: string): Promise<void>;
 }
 
 // 缓存数据源接口