feat(apple): saved devices and targeted transfers UI

Adds the native SwiftUI Saved Devices experience on top of the production
saved-device core, as a top-level destination in the iOS tab bar and the
macOS sidebar.

Core seam:
- App-facing saved-device domain models mirroring core/SavedDeviceModels.kt,
  with lifecycle helpers (canReceive/canResume/canCancel/canDelete) so views
  never hand-roll state checks.
- 21 gateway methods through CoreGateway/CoreRepository with UniFFI mapping.
  cancelTargetedTransfer, forgetSavedDevice and blockDevice run off the serial
  lane: each must reach the core while a targeted receive is blocking it.
- Payload-free pairingChanged/targetedTransferChanged signals, dispatched
  before the numeric-transferId guard since saved-device events identify
  their subject by peer endpoint or a string transfer id.

Experience:
- Screen lists saved devices and outstanding consent requests only; the
  global targeted-transfer history stays out, reachable per device.
- Details as a sheet with detents on compact layouts and a native inspector
  on macOS, owning Send, label, forget/block and that device's transfers.
- Label editing is transactional: the draft and editor survive a failed
  write, conflicting actions are refused while saving, and the editor closes
  only after the core confirms.
- Pairing and targeted-offer consent hosted at the app root, answerable from
  any tab and suppressed while a transfer approval is up. Dismissing a
  pairing prompt suppresses locally without consuming the single-use
  eligibility; dismissing an offer declines it, since an unanswered offer
  holds a slot in the core's bounded per-sender queue.
- Targeted send reuses the invitation composer's affordances with file,
  folder, rename, replace and cleanup parity. Picker copies are released on
  replace/remove/clear/cancel and after a successful create, but kept after a
  failure so retry does not require re-picking.
- Notifications for pairing requests and offers (withdrawn once answered) and
  for terminal targeted transfers. Wording follows direction: on the sending
  device the peer finished receiving, not us.

Localization:
- Widens 52 saved-device keys from kmp-only to both platforms.
- Five keys carried a literal %1$s with no declared args, which Compose
  renders positionally but the Apple generator emits as a plain constant,
  leaking the placeholder into the UI. They now use named args; Compose
  output is byte-identical.
- Adds targeted_offer_title/body. Reusing the invitation approval copy stated
  the roles backwards, announcing the sender as the receiver.

Also surfaces core startup failures: the startup overlay is drawn above the
snackbar host, so a failed initialize() was indistinguishable from an app
that never finished loading. AppModel now keeps the reason, logs it, and the
overlay shows it with a retry, plus the technical detail in DEBUG builds.

Send and receive between two devices is verified only partially; a missing
endpoint-identity credential currently blocks startup on the test device.

apple/VniDrop/Platform/FileSystemService+macOS.swift

@@ -44,10 +44,42 @@ struct MacFileSystemService: FileSystemService {
 		guard !files.isEmpty else {
 			return .failure(InvitationError.shareEmpty)
 		}
-		// Re-acquire security-scoped access to every picked source (from the bookmark
-		// captured at pick time) and hold it across the whole share call. The core
-		// imports the bytes during shareFiles(), so access only needs to survive that
-		// call; without this, the import fails with EPERM under the App Store sandbox.
+		guard case .invitation(let accessPolicy) = destination else {
+			return .failure(InvitationError.unsupportedOperation)
+		}
+		return await withScopedSources(files) { sources in
+			await repository.shareSources(
+				sources, transferName: transferName, senderName: senderName, accessPolicy: accessPolicy
+			)
+		}
+	}
+
+	func sendPickedFilesToSavedDevice(
+		repository: CoreGateway,
+		files: [PickedShareFile],
+		transferName: String,
+		receiverEndpointId: String
+	) async -> Result<TargetedTransferModel, Error> {
+		guard !files.isEmpty else {
+			return .failure(InvitationError.shareEmpty)
+		}
+		return await withScopedSources(files) { sources in
+			await repository.createTargetedTransfer(
+				receiverEndpointId: receiverEndpointId,
+				sources: sources,
+				transferName: transferName.isEmpty ? nil : transferName
+			)
+		}
+	}
+
+	/// Re-acquires security-scoped access to every picked source (from the bookmark
+	/// captured at pick time) and holds it across `body`. The core imports the bytes
+	/// during that call, so access only needs to survive it; without this the import
+	/// fails with EPERM under the App Store sandbox.
+	private func withScopedSources<T>(
+		_ files: [PickedShareFile],
+		_ body: ([ShareSource]) async -> Result<T, Error>
+	) async -> Result<T, Error> {
 		var scopedURLs: [URL] = []
 		for file in files {
 			guard let bookmark = file.securityScopeBookmark else { continue }
@@ -63,12 +95,7 @@ struct MacFileSystemService: FileSystemService {
 		let sources = files.map {
 			ShareSource(kind: .path, value: $0.value, displayName: $0.displayName, isDirectory: $0.isDirectory)
 		}
-		guard case .invitation(let accessPolicy) = destination else {
-			return .failure(InvitationError.unsupportedOperation)
-		}
-		return await repository.shareSources(
-			sources, transferName: transferName, senderName: senderName, accessPolicy: accessPolicy
-		)
+		return await body(sources)
 	}
 }
 #endif