feat: implement account switcher component and state management

- Add AccountSwitcher component for managing user accounts with UI for switching, adding, and logging out.
- Create account state manager to handle snapshots of account-specific states for efficient switching.
- Introduce utility functions for account management, including ID generation and avatar color assignment.
- Implement Zustand store for account management, supporting addition, removal, and state retrieval of accounts.

app/[locale]/calendar/page.tsx

@@ -712,7 +712,7 @@ export default function CalendarPage() {
             collapsed
             quota={quota}
             isPushConnected={isPushConnected}
-            onLogout={() => { logout(); router.push('/login'); }}
+            onLogout={() => { logout(); if (!useAuthStore.getState().isAuthenticated) router.push('/login'); }}
             onManageApps={handleManageApps}
             onInlineApp={handleInlineApp}
             onCloseInlineApp={closeInlineApp}