test(apple): CoreGateway seam, XCTest suite, and CI

- Introduce a CoreGateway protocol so feature models depend on a seam
  (CoreRepository conforms); enables faking the core in tests
- Add a VniDropTests target with 42 tests mirroring the KMP suites:
  approval coordinator, send/receive/settings/app models, preferences,
  file previews, invitation decode, message queue, error mapping
- Add a fake gateway/file-system/device-info and fixtures
- Add .github/workflows/apple.yml: build the Rust core, generate the
  project, and run the tests on an iOS Simulator

apple/VniDrop/Features/App/AppModel.swift

@@ -9,13 +9,13 @@ final class AppModel: ObservableObject {
 	@Published private(set) var themeMode: ThemeMode = .system
 
 	private let environment: PlatformEnvironment
-	private let repository: CoreRepository
+	private let repository: CoreGateway
 	private let messages: UiMessageController
 	private var cancellables = Set<AnyCancellable>()
 
 	init(
 		environment: PlatformEnvironment,
-		repository: CoreRepository,
+		repository: CoreGateway,
 		preferences: AppPreferencesRepository,
 		messages: UiMessageController
 	) {

apple/VniDrop/Features/Approvals/ApprovalCoordinator.swift

@@ -26,7 +26,7 @@ struct ApprovalState: Equatable {
 final class ApprovalCoordinator: ObservableObject {
 	@Published private(set) var state = ApprovalState()
 
-	private let repository: CoreRepository
+	private let repository: CoreGateway
 	private let preferences: AppPreferencesRepository
 	private let notifications: LocalNotificationService
 	private let visibility: AppVisibility
@@ -36,7 +36,7 @@ final class ApprovalCoordinator: ObservableObject {
 	private var cancellables = Set<AnyCancellable>()
 
 	init(
-		repository: CoreRepository,
+		repository: CoreGateway,
 		preferences: AppPreferencesRepository,
 		notifications: LocalNotificationService,
 		visibility: AppVisibility,
@@ -57,7 +57,7 @@ final class ApprovalCoordinator: ObservableObject {
 			}
 			.store(in: &cancellables)
 
-		repository.$state
+		repository.statePublisher
 			.sink { [weak self] core in
 				guard let self, core.isInitialized else { return }
 				let sharing = core.transfers.filter { $0.direction == .send && $0.status == .sharing }

apple/VniDrop/Features/Receive/ReceiveModel.swift

@@ -51,13 +51,13 @@ final class ReceiveModel: ObservableObject {
 	@Published private(set) var state = ReceiveState()
 	@Published private(set) var coreState = CoreState()
 
-	private let repository: CoreRepository
+	private let repository: CoreGateway
 	private let fileSystemService: FileSystemService
 	private let messages: UiMessageController
 	private var cancellables = Set<AnyCancellable>()
 
 	init(
-		repository: CoreRepository,
+		repository: CoreGateway,
 		fileSystemService: FileSystemService,
 		preferences: AppPreferencesRepository,
 		messages: UiMessageController
@@ -66,7 +66,7 @@ final class ReceiveModel: ObservableObject {
 		self.fileSystemService = fileSystemService
 		self.messages = messages
 
-		repository.$state.sink { [weak self] in self?.coreState = $0 }.store(in: &cancellables)
+		repository.statePublisher.sink { [weak self] in self?.coreState = $0 }.store(in: &cancellables)
 
 		preferences.$preferences
 			.sink { [weak self] prefs in

apple/VniDrop/Features/Send/SendModel.swift

@@ -50,14 +50,14 @@ final class SendModel: ObservableObject {
 	/// small transfer complete.
 	@Published private(set) var receiversByTransfer: [UInt64: [ReceiverRequestModel]] = [:]
 
-	private let repository: CoreRepository
+	private let repository: CoreGateway
 	private let fileSystemService: FileSystemService
 	private let filePreviewRepository: FilePreviewRepository
 	private let messages: UiMessageController
 	private var cancellables = Set<AnyCancellable>()
 
 	init(
-		repository: CoreRepository,
+		repository: CoreGateway,
 		fileSystemService: FileSystemService,
 		preferences: AppPreferencesRepository,
 		filePreviewRepository: FilePreviewRepository,
@@ -68,7 +68,7 @@ final class SendModel: ObservableObject {
 		self.filePreviewRepository = filePreviewRepository
 		self.messages = messages
 
-		repository.$state.sink { [weak self] in self?.coreState = $0 }.store(in: &cancellables)
+		repository.statePublisher.sink { [weak self] in self?.coreState = $0 }.store(in: &cancellables)
 
 		repository.signals
 			.sink { [weak self] signal in
@@ -86,7 +86,7 @@ final class SendModel: ObservableObject {
 		// Keep receiver delivery records current for every sharing/importing
 		// outgoing transfer (new shares appear here; status transitions arrive via
 		// the receiverHistoryChanged signal above).
-		repository.$state
+		repository.statePublisher
 			.map { core -> Set<UInt64> in
 				Set(core.transfers
 					.filter { $0.direction == .send && ($0.status == .sharing || $0.status == .importing) }
@@ -100,7 +100,7 @@ final class SendModel: ObservableObject {
 			.sink { [weak self] previews in self?.state.transferThumbnails = previews }
 			.store(in: &cancellables)
 
-		repository.$state
+		repository.statePublisher
 			.map { core -> Set<UInt64>? in
 				core.isInitialized ? Set(core.transfers.map(\.transferId)) : nil
 			}

apple/VniDrop/Features/Settings/SettingsModel.swift

@@ -85,7 +85,7 @@ final class SettingsModel: ObservableObject {
 	private let environment: PlatformEnvironment
 	private let deviceInfoProvider: DeviceInfoProvider
 	private let fileSystemService: FileSystemService
-	private let repository: CoreRepository
+	private let repository: CoreGateway
 	private let preferences: AppPreferencesRepository
 	private let notifications: LocalNotificationService
 	private let messages: UiMessageController
@@ -101,7 +101,7 @@ final class SettingsModel: ObservableObject {
 		environment: PlatformEnvironment,
 		deviceInfoProvider: DeviceInfoProvider,
 		fileSystemService: FileSystemService,
-		repository: CoreRepository,
+		repository: CoreGateway,
 		preferences: AppPreferencesRepository,
 		notifications: LocalNotificationService,
 		messages: UiMessageController,