- Add WebDavSyncService.canSync() as single source of truth
- Add SyncGateResult data class for structured response
- Update MainViewModel.triggerManualSync() to use canSync()
- Update MainViewModel.triggerAutoSync() to use canSync() - FIXES onResume bug
- Update NoteEditorViewModel.triggerOnSaveSync() to use canSync()
- Update SettingsViewModel.syncNow() to use canSync()
- Update SyncWorker to use canSync() instead of direct prefs check
All 9 sync paths now respect WiFi-only setting through one central gate.