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.