Add new button to check and display current session status:
- New checkSessionStatus() function in useAuthentik composable
- Displays toast notification with session info
- Shows user name if authenticated or warning if not
- Add UNotifications component to app.vue to render toasts
This allows users to quickly verify their authentication status.
- Resolve SSR error "useAuthentik is not defined"
- Follow Nuxt 4 directory structure conventions
- When app/ exists, all app directories must be inside it
- This enables proper auto-import of composables
