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/Tests/SendModelTests.swift

@@ -0,0 +1,58 @@
+import XCTest
+@testable import VniDrop
+
+/// Ports the send-side state-machine assertions from `feature/ViewModelsTest.kt`.
+@MainActor
+final class SendModelTests: XCTestCase {
+
+	private func makeModel(_ core: FakeCoreGateway) -> SendModel {
+		SendModel(
+			repository: core,
+			fileSystemService: FakeFileSystemService(),
+			preferences: Fixtures.preferences(),
+			filePreviewRepository: FilePreviewRepository(appDataDir: NSTemporaryDirectory() + UUID().uuidString),
+			messages: UiMessageController()
+		)
+	}
+
+	func testOpenAndCloseTransferDetails() {
+		let model = makeModel(FakeCoreGateway())
+		model.openTransfer(3)
+		XCTAssertEqual(model.state.selectedTransferId, 3)
+		model.closeTransferDetails()
+		XCTAssertNil(model.state.selectedTransferId)
+	}
+
+	func testDeleteTransferConfirmationFlow() async {
+		let core = FakeCoreGateway()
+		let model = makeModel(core)
+		model.openTransfer(3)
+
+		model.requestDeleteTransfer()
+		XCTAssertTrue(model.state.isDeleteConfirmationOpen)
+
+		model.confirmDeleteTransfer()
+		await waitUntil { core.deletedTransfers.contains(3) }
+		XCTAssertEqual(core.deletedTransfers, [3])
+		XCTAssertNil(model.state.selectedTransferId)
+		XCTAssertFalse(model.state.isDeleteConfirmationOpen)
+	}
+
+	func testStopSharingCancelsTheTransfer() async {
+		let core = FakeCoreGateway()
+		let model = makeModel(core)
+		model.stopSharing(transferId: 4)
+		await waitUntil { core.cancelledTransfers.contains(4) }
+		XCTAssertEqual(core.cancelledTransfers, [4])
+	}
+
+	func testCancelReceiverRefusesTheRequest() async {
+		let core = FakeCoreGateway()
+		let model = makeModel(core)
+		model.openTransfer(1)
+		model.cancelReceiver(requestId: "req-1")
+		await waitUntil { core.responses.contains { $0.id == "req-1" } }
+		let response = core.responses.first { $0.id == "req-1" }
+		XCTAssertEqual(response?.accepted, false)
+	}
+}