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/screens/message/PrivateChatInfoScreen.tsx

@@ -22,8 +22,8 @@ import { authService } from '@/services/auth';
 import { messageService } from '@/services/message';
 import { ApiError } from '@/services/core';
 import { messageRepository, conversationRepository } from '@/database';
-import { messageManager } from '../../stores/messageManager';
-import { userManager } from '../../stores/userManager';
+import { messageManager } from '../../stores/message';
+import { userManager } from '../../stores/user';
 import { Avatar, Text, Button, Loading, Divider } from '../../components/common';
 import { User } from '../../types';
 import * as hrefs from '../../navigation/hrefs';