feat(ui): add emoji picker with FlatList virtualization and improve input components

- Add full emoji picker with virtualized FlatList to CreatePostScreen and PostDetailScreen
- Add autoExpand prop to PostMentionInput for XHS-style content area
- Improve mention item styling with @ icon and hint text
- Fix HomeScreen tab switching race condition with requestAnimationFrame
- Fix PostRepository pagination to prefer cursor over page parameter
- Fix user store imports to use explicit UserManager path
- Refactor useCurrentUser hook to use sessionStore directly

src/stores/call/callStore.ts

@@ -10,7 +10,7 @@ import {
 import { webrtcManager, ICEServer } from '@/services/webrtc';
 import { getCurrentUserId } from '../auth/sessionStore';
 import { useUserStore } from '../userStore';
-import { userManager } from '../user';
+import { userManager } from '../user/UserManager';
 
 export type CallStatus = 
   | 'idle'           // 空闲状态