feat(apple): local notifications for transfer lifecycle events

Adds background notifications for the "the thing you were waiting for is
done" moments, alongside the existing incoming-approval-request one:

  - a receive finished downloading            (receive -> done)
  - a receive failed / was interrupted         (receive -> failed)
  - a share you own failed                      (send -> failed)
  - a receiver finished downloading your share  (receiver status completed)

A new TransferNotificationCoordinator observes core state + signals and
publishes these; the decision of which moments notify is a pure function
(plannedTransferNotifications / plannedReceiverNotifications), unit-tested
independently. The first state snapshot only primes existing history as seen
so launch doesn't spam.

Notification permission is now the single source of truth. The in-app
notifications toggle and its decoupled UserDefaults preference are gone;
the Settings section shows an "Allow notifications" button that requests the
OS permission (or deep-links to Settings once decided), and notifications
gate purely on `permission == .granted`.

macOS delivery fixes:
  - add a UNUserNotificationCenterDelegate so banners present even while the
    app is active (the app window is usually open on macOS)
  - present-when-active on macOS, suppress-when-foregrounded on iOS
  - reserve the notification id before awaiting publish: the CombineLatest
    fired several times and re-added the same identifier, which macOS
    coalesces into a silent update with no banner
  - LocalNotificationService seeds its permission at init so gating can't
    race a not-yet-refreshed .notDetermined

Eight localized title/body strings added (apple-only); the shared
notifications_description copy is generalized from "receive requests" to
"transfer activity".

apple/VniDrop/App/AppGraph.swift

@@ -12,6 +12,7 @@ final class AppGraph: ObservableObject {
 	let preferencesRepository: AppPreferencesRepository
 	let filePreviewRepository: FilePreviewRepository
 	let approvalCoordinator: ApprovalCoordinator
+	let transferNotificationCoordinator: TransferNotificationCoordinator
 
 	init(dependencies: AppDependencies, coreRepository: CoreRepository? = nil) {
 		self.dependencies = dependencies
@@ -23,13 +24,17 @@ final class AppGraph: ObservableObject {
 				username: dependencies.environment.defaultUsername,
 				receiveFolder: dependencies.fileSystemService.defaultReceiveFolder(),
 				themeMode: .system,
-				notificationsEnabled: false,
 				diagnosticsEnabled: false
 			)
 		)
 		self.approvalCoordinator = ApprovalCoordinator(
 			repository: coreRepository,
-			preferences: preferencesRepository,
+			notifications: dependencies.notificationService,
+			visibility: visibility,
+			messages: messages
+		)
+		self.transferNotificationCoordinator = TransferNotificationCoordinator(
+			repository: coreRepository,
 			notifications: dependencies.notificationService,
 			visibility: visibility,
 			messages: messages