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- Notifications for pairing requests and offers (withdrawn once answered) and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/Core/CoreModels.swift

@@ -47,6 +47,12 @@ enum EventPhase: String, Equatable, Sendable {
 	case network
 	case handshake
 	case error
+	/// Saved-device consent lifecycle (eligibility, relationships, grants).
+	case pairing
+	/// Targeted-transfer offer and lifecycle. Its events identify the transfer by
+	/// a string `targeted_transfer_id`, not the numeric `transferId` used by
+	/// invitation shares.
+	case targetedTransfer = "targeted_transfer"
 }
 
 /// Kind of a core progress event (the `kind` wire field).
@@ -174,6 +180,13 @@ enum CoreSignal: Equatable, Sendable {
 	case receiverHistoryChanged(transferId: UInt64)
 	/// Transfer status/history changed enough to re-read the durable snapshot.
 	case transfersChanged(transferId: UInt64)
+	/// Pairing / saved-device state changed; refresh eligibility, relationships,
+	/// and the saved list. Carries no payload: core events are wake-ups, not
+	/// authoritative state, so consumers re-query rather than apply a delta.
+	case pairingChanged
+	/// Targeted-transfer offer or lifecycle changed; refresh pending offers and
+	/// transfers. Payload-free for the same reason as `pairingChanged`.
+	case targetedTransferChanged
 }
 
 // MARK: - Transfer helpers (ported from AppUiModels.kt)