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/user/hooks.ts

@@ -2,7 +2,7 @@ import { useCallback, useEffect, useRef } from 'react';
 import { useUserManagerStore } from './userStore';
 import { userManager } from './UserManager';
 import type { UserDTO } from '../../types/dto';
-import { useAuthStore } from '../authStore';
+import { useAuthStore } from '../auth/authStore';
 
 export interface UseCurrentUserResult {
   user: UserDTO | null;