feat(apple): native SwiftUI app for iOS and macOS

Add a native SwiftUI VniDrop app (Send/Receive/Settings) talking to the
Rust core via generated UniFFI Swift bindings, plus the uniffi-bindgen
helper crate. iOS uses a TabView, macOS a NavigationSplitView sidebar.

apple/VniDrop/App/RootView.swift

@@ -0,0 +1,169 @@
+import SwiftUI
+
+/// App root, ported from `App.kt`. Owns the object graph and feature models, wires
+/// the adaptive shell, floating actions, snackbar host, and approval modal.
+struct RootView: View {
+	@StateObject private var graph: AppGraph
+	@StateObject private var appModel: AppModel
+	@StateObject private var sendModel: SendModel
+	@StateObject private var receiveModel: ReceiveModel
+	@StateObject private var settingsModel: SettingsModel
+	@ObservedObject private var messages: UiMessageController
+	@ObservedObject private var approvals: ApprovalCoordinator
+
+	@Environment(\.scenePhase) private var scenePhase
+
+	init(dependencies: AppDependencies) {
+		let graph = AppGraph(dependencies: dependencies)
+		_graph = StateObject(wrappedValue: graph)
+		_appModel = StateObject(wrappedValue: AppModel(
+			environment: dependencies.environment,
+			repository: graph.coreRepository,
+			preferences: graph.preferencesRepository,
+			messages: graph.messages
+		))
+		_sendModel = StateObject(wrappedValue: SendModel(
+			repository: graph.coreRepository,
+			fileSystemService: dependencies.fileSystemService,
+			preferences: graph.preferencesRepository,
+			filePreviewRepository: graph.filePreviewRepository,
+			messages: graph.messages
+		))
+		_receiveModel = StateObject(wrappedValue: ReceiveModel(
+			repository: graph.coreRepository,
+			fileSystemService: dependencies.fileSystemService,
+			preferences: graph.preferencesRepository,
+			messages: graph.messages
+		))
+		_settingsModel = StateObject(wrappedValue: SettingsModel(
+			environment: dependencies.environment,
+			deviceInfoProvider: dependencies.deviceInfoProvider,
+			fileSystemService: dependencies.fileSystemService,
+			preferences: graph.preferencesRepository,
+			notifications: dependencies.notificationService,
+			messages: graph.messages,
+			bugReports: NoopBugReportService()
+		))
+		messages = graph.messages
+		approvals = graph.approvalCoordinator
+	}
+
+	var body: some View {
+		GeometryReader { proxy in
+			let windowClass = windowClassFor(width: proxy.size.width)
+			let isDark = resolveDarkTheme(appModel.themeMode, systemDark: systemDark)
+			ZStack {
+				navigation(windowClass: windowClass)
+				SnackbarHost(controller: messages)
+				ApprovalModalHost(
+					state: approvals.state,
+					onAccept: approvals.accept,
+					onRefuse: approvals.refuse
+				)
+			}
+			.vniDropTheme(isDark: isDark)
+			.preferredColorScheme(appModel.themeMode.preferredColorScheme)
+			.environment(\.vniColors, isDark ? .dark : .light)
+		}
+		.platformPickers(settingsModel: settingsModel)
+		.task { await consumeExternalInvitations() }
+		.onChange(of: scenePhase) { phase in
+			switch phase {
+			case .active:
+				graph.visibility.setForeground(true)
+				settingsModel.refreshNotificationPermission()
+				// Reconcile against the durable snapshot: while the window was
+				// unfocused/occluded (common on macOS) live events may not have
+				// rendered, leaving progress/status stale.
+				Task { _ = await graph.coreRepository.refresh() }
+			case .background, .inactive:
+				graph.visibility.setForeground(false)
+			@unknown default:
+				break
+			}
+		}
+	}
+
+	/// iOS uses a bottom tab bar; macOS uses a native source-list sidebar so each
+	/// screen's toolbar lives in the detail column instead of the shared title bar.
+	@ViewBuilder
+	private func navigation(windowClass: WindowClass) -> some View {
+		#if os(macOS)
+		NavigationSplitView {
+			List(AppDestination.allCases, selection: sidebarBinding) { destination in
+				Label(LocalizedStringKey(destination.labelKey), systemImage: destination.systemImage)
+					.tag(destination)
+			}
+			.navigationSplitViewColumnWidth(min: 180, ideal: 200, max: 260)
+		} detail: {
+			screen(for: appModel.destination, windowClass: windowClass)
+		}
+		#else
+		TabView(selection: destinationBinding) {
+			ForEach(AppDestination.allCases) { destination in
+				screen(for: destination, windowClass: windowClass)
+					.tabItem {
+						Label(LocalizedStringKey(destination.labelKey), systemImage: destination.systemImage)
+					}
+					.tag(destination)
+			}
+		}
+		#endif
+	}
+
+	private var sidebarBinding: Binding<AppDestination?> {
+		Binding(
+			get: { appModel.destination },
+			set: { newValue in
+				if let value = newValue {
+					Task { @MainActor in appModel.selectDestination(value) }
+				}
+			}
+		)
+	}
+
+	private var destinationBinding: Binding<AppDestination> {
+		// Defer the write out of the current view-update cycle: TabView reconciles
+		// its selection synchronously during body evaluation on macOS, and mutating
+		// the published `destination` there triggers a "publishing within view
+		// updates" warning.
+		Binding(get: { appModel.destination }, set: { newValue in
+			Task { @MainActor in appModel.selectDestination(newValue) }
+		})
+	}
+
+	@ViewBuilder
+	private func screen(for destination: AppDestination, windowClass: WindowClass) -> some View {
+		switch destination {
+		case .send: SendScreen(model: sendModel, windowClass: windowClass)
+		case .receive: ReceiveScreen(model: receiveModel, windowClass: windowClass)
+		case .settings: SettingsScreen(model: settingsModel, windowClass: windowClass)
+		}
+	}
+
+	private var systemDark: Bool {
+		#if os(iOS)
+		return UITraitCollection.current.userInterfaceStyle == .dark
+		#else
+		return NSApp.effectiveAppearance.bestMatch(from: [.darkAqua, .aqua]) == .darkAqua
+		#endif
+	}
+
+	private func consumeExternalInvitations() async {
+		for await invitation in graph.dependencies.externalInvitations.invitations {
+			appModel.selectDestination(.receive)
+			switch invitation {
+			case .success(let raw):
+				receiveModel.onInvitationResult(.invitationFile, .success(raw))
+			case .failure(let error):
+				receiveModel.onInvitationResult(.invitationFile, .failure(error))
+			}
+		}
+	}
+}
+
+#if os(iOS)
+import UIKit
+#else
+import AppKit
+#endif