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/settings/index.ts

@@ -0,0 +1,26 @@
+/**
+ * 设置模块统一导出
+ */
+
+export {
+  useChatSettingsStore,
+  useChatSettingsActions,
+  useChatFontSize,
+  useChatMessageRadius,
+  useChatTheme,
+  useChatNightMode,
+  CHAT_THEMES,
+} from './chatSettingsStore';
+export type { ChatSettings, ChatThemeId } from './chatSettingsStore';
+
+export {
+  useAppColors,
+  useThemePreference,
+  useResolvedColorScheme,
+  useSetThemePreference,
+  usePaperThemeFromStore,
+  ThemeBootstrap,
+  useThemeStore,
+  getSystemScheme,
+} from './themeStore';
+export type { ThemePreference, ResolvedScheme } from './themeStore';