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/components/ChatScreen/useChatScreen.ts

@@ -28,8 +28,8 @@ import { ApiError } from '@/services/core';
 // 【新架构】使用 MessageManager
 import { useChat, useGroupTyping, useGroupMuted, messageManager, callStore } from '../../../../stores';
 import { groupService } from '@/services/message';
-import { userManager } from '../../../../stores/userManager';
-import { groupManager } from '../../../../stores/groupManager';
+import { userManager } from '../../../../stores/user';
+import { groupManager } from '../../../../stores/group';
 import * as hrefs from '../../../../navigation/hrefs';
 import { firstRouteParam } from '../../../../navigation/paramUtils';
 import {