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/AppEnvironment.swift

@@ -0,0 +1,31 @@
+import Foundation
+
+/// Platform environment, ported from `Platform.kt` (`PlatformEnvironment`).
+struct PlatformEnvironment {
+	let name: String
+	let appVersion: String
+	let defaultCoreDataDir: String
+	var defaultUsername: String = "Receiver"
+}
+
+/// Device info for diagnostics/about, ported from `DeviceInfo`.
+struct DeviceInfo {
+	let deviceName: String?
+	let deviceModel: String?
+	let operatingSystem: String
+	let network: String?
+	let batteryLevel: String?
+}
+
+protocol DeviceInfoProvider {
+	func load() async -> DeviceInfo
+}
+
+/// Bundle of platform dependencies, ported from `AppDependencies`.
+struct AppDependencies {
+	let environment: PlatformEnvironment
+	let deviceInfoProvider: DeviceInfoProvider
+	let fileSystemService: FileSystemService
+	let notificationService: LocalNotificationService
+	let externalInvitations: ExternalInvitationController
+}