OfflineQueueService - IndexedDB-backed service for queuing offline actions

Provides persistent storage for actions that need to be synced when online. Uses IndexedDB for reliable cross-session persistence.

Features:

• Queue actions for later sync
• Persist across browser sessions
• Automatic sync when coming online
• Progress callbacks during sync
• Error tracking for failed actions
• CSRF token refresh before sync

RsvpCacheService - IndexedDB-backed service for caching user RSVPs

Provides local storage for user's RSVPs to enable offline viewing and offline RSVP creation. Syncs with server when online.

Features:

• Cache user's RSVPs for offline access
• Store pending RSVPs when offline
• Sync pending RSVPs when coming online
• Update cache when user changes RSVPs