- completedMonthKeys: remove UserDefaults-based MonthlyCheckInStore check (not synced via iCloud)
- MonthlyCheckInCard.effectiveLastCheckInDate: use max() instead of ?? to prefer newer synced snapshot date
- MonthlyCheckInView.lastCompletionDate: use max() of local + latest CoreData snapshot via @FetchRequest
- FirebaseService.logPaywallShown: fix parameter key to paywall_trigger (matches GA4 custom dimension)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>