refactor(stores): reorganize flat store files into modular directory structure

Migrate from flat file organization to modular directory structure under src/stores/:

- auth/: authStore, registerStore, verificationStore, sessionStore
- call/: callStore
- settings/: chatSettingsStore, themeStore
- ui/: homeTabBarVisibilityStore, homeTabPressStore
- utils/: routePayloadCache
- group/sources.ts, group/profileResolver.ts
- message/sources.ts
- post/sources.ts

Update all import paths across components and screens to use new module paths. Maintain backward compatibility through deprecated re-export files for gradual migration.

src/stores/message/services/MessageSyncService.ts

@@ -16,7 +16,7 @@ import {
   SqliteConversationListPagedSource,
   createRemoteConversationListSource,
   CONVERSATION_LIST_PAGE_SIZE,
-} from '../../conversationListSources';
+} from '../sources';
 import type { IMessageSyncService, MessageManagerConversationListDeps, IUserCacheService } from '../types';
 import { useMessageStore, normalizeConversationId, mergeMessagesById } from '../store';
 import { ReadReceiptManager } from './ReadReceiptManager';