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/Platform/AppDependencies+macOS.swift

@@ -0,0 +1,50 @@
+#if os(macOS)
+import Foundation
+import AppKit
+
+/// Builds the macOS dependency graph, mirroring `rememberIosAppDependencies`.
+@MainActor
+func makeAppDependencies(externalInvitations: ExternalInvitationController) -> AppDependencies {
+	let version = Bundle.main.object(forInfoDictionaryKey: "CFBundleShortVersionString") as? String ?? "0.1.0"
+	let host = Host.current().localizedName ?? "Mac"
+	let env = PlatformEnvironment(
+		name: "macOS " + ProcessInfo.processInfo.operatingSystemVersionString,
+		appVersion: version,
+		defaultCoreDataDir: applicationDataDirectory(),
+		defaultUsername: host
+	)
+	return AppDependencies(
+		environment: env,
+		deviceInfoProvider: MacDeviceInfoProvider(),
+		fileSystemService: MacFileSystemService(),
+		notificationService: LocalNotificationService(),
+		externalInvitations: externalInvitations
+	)
+}
+
+private func applicationDataDirectory() -> String {
+	let base = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first!
+	return base.appendingPathComponent("VniDrop").path
+}
+
+private struct MacDeviceInfoProvider: DeviceInfoProvider {
+	func load() async -> DeviceInfo {
+		DeviceInfo(
+			deviceName: Host.current().localizedName,
+			deviceModel: modelIdentifier(),
+			operatingSystem: "macOS " + ProcessInfo.processInfo.operatingSystemVersionString,
+			network: nil,
+			batteryLevel: nil
+		)
+	}
+
+	private func modelIdentifier() -> String? {
+		var size = 0
+		sysctlbyname("hw.model", nil, &size, nil, 0)
+		guard size > 0 else { return nil }
+		var model = [CChar](repeating: 0, count: size)
+		sysctlbyname("hw.model", &model, &size, nil, 0)
+		return String(cString: model)
+	}
+}
+#endif