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/ApprovalCoordinatorTests.swift

@@ -0,0 +1,69 @@
+import XCTest
+import Combine
+@testable import VniDrop
+
+/// Ports `feature/approvals/ApprovalCoordinatorTest.kt` (the gateway-observable
+/// parts; notification assertions require a notification-service seam we don't
+/// have on Apple yet).
+@MainActor
+final class ApprovalCoordinatorTests: XCTestCase {
+
+	private func makeCoordinator(_ core: FakeCoreGateway) -> ApprovalCoordinator {
+		ApprovalCoordinator(
+			repository: core,
+			preferences: Fixtures.preferences(),
+			notifications: LocalNotificationService(),
+			visibility: AppVisibility(),
+			messages: UiMessageController()
+		)
+	}
+
+	func testOrdersPendingRequestsByRequestedAt() async {
+		let core = FakeCoreGateway()
+		core.requests[1] = [Fixtures.request(id: "new", requestedAt: 20),
+							 Fixtures.request(id: "old", requestedAt: 10)]
+		let coordinator = makeCoordinator(core)
+
+		core.setState(CoreState(isInitialized: true, transfers: [Fixtures.transfer(id: 1, direction: .send, status: .sharing)]))
+		core.emit(.approvalChanged(transferId: 1))
+
+		await waitUntil { !coordinator.state.pending.isEmpty }
+		XCTAssertEqual(coordinator.state.pending.map(\.id), ["old", "new"])
+		XCTAssertEqual(coordinator.state.current?.id, "old")
+	}
+
+	func testFailedResponseKeepsRequestVisibleAndClearsResponding() async {
+		let core = FakeCoreGateway()
+		core.requests[1] = [Fixtures.request(id: "request", requestedAt: 10)]
+		core.responseResult = .failure(TestError.unimplemented)
+		let coordinator = makeCoordinator(core)
+
+		core.setState(CoreState(isInitialized: true, transfers: [Fixtures.transfer(id: 1, direction: .send, status: .sharing)]))
+		core.emit(.approvalChanged(transferId: 1))
+		await waitUntil { coordinator.state.pending.contains { $0.id == "request" } }
+
+		coordinator.accept("request")
+		await waitUntil { coordinator.state.respondingIds.isEmpty && core.responses.count == 1 }
+
+		XCTAssertTrue(coordinator.state.pending.contains { $0.id == "request" })
+		XCTAssertTrue(coordinator.state.respondingIds.isEmpty)
+		XCTAssertEqual(core.responses.first?.accepted, true)
+	}
+
+	func testAcceptRespondsPositivelyAndSingleFlights() async {
+		let core = FakeCoreGateway()
+		core.requests[1] = [Fixtures.request(id: "request", requestedAt: 10)]
+		let coordinator = makeCoordinator(core)
+		core.setState(CoreState(isInitialized: true, transfers: [Fixtures.transfer(id: 1, direction: .send, status: .sharing)]))
+		core.emit(.approvalChanged(transferId: 1))
+		await waitUntil { coordinator.state.current != nil }
+
+		coordinator.accept("request")
+		coordinator.accept("request") // second call must be ignored (single-flight)
+		await waitUntil { core.responses.count >= 1 }
+		try? await Task.sleep(nanoseconds: 50_000_000)
+
+		XCTAssertEqual(core.responses.count, 1)
+		XCTAssertEqual(core.responses.first?.id, "request")
+	}
+}