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/schedule/CourseDetailScreen.tsx

@@ -5,7 +5,7 @@ import { useRouter, useLocalSearchParams } from 'expo-router';
 import { MaterialCommunityIcons } from '@expo/vector-icons';
 
 import { spacing, borderRadius, fontSizes, shadows, useAppColors, type AppColors } from '../../theme';
-import { routePayloadCache } from '../../stores/routePayloadCache';
+import { routePayloadCache } from '../../stores';
 import { scheduleService } from '@/services/platform';
 
 const WEEKDAY_NAMES = ['周一', '周二', '周三', '周四', '周五', '周六', '周日'];

src/screens/schedule/ScheduleScreen.tsx

@@ -42,7 +42,7 @@ import {
   hasCourseInWeek,
 } from '../../types/schedule';
 import * as hrefs from '../../navigation/hrefs';
-import { routePayloadCache } from '../../stores/routePayloadCache';
+import { routePayloadCache } from '../../stores';
 import { scheduleService } from '@/services/platform';
 
 const { width: SCREEN_WIDTH } = Dimensions.get('window');