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/Package.swift

@@ -0,0 +1,43 @@
+// swift-tools-version:5.9
+import PackageDescription
+
+// Core/UI Swift sources built as a library so the shared logic can be typechecked
+// and unit-tested from the command line (macOS). The iOS/macOS app target in the
+// Xcode project links the same sources plus the app entry point.
+let package = Package(
+	name: "VniDropApp",
+	defaultLocalization: "en",
+	platforms: [
+		.iOS(.v16),
+		.macOS(.v13),
+	],
+	products: [
+		.library(name: "VniDropApp", targets: ["VniDropApp"]),
+	],
+	dependencies: [
+		.package(path: "VnidropCore"),
+	],
+	targets: [
+		.target(
+			name: "VniDropApp",
+			dependencies: [.product(name: "VnidropCore", package: "VnidropCore")],
+			path: "VniDrop",
+			// The @main entry belongs to the Xcode app target only; excluding it
+			// keeps this library free of a conflicting `_main` symbol for tests.
+			exclude: ["Resources", "App/VniDropApp.swift"],
+			// The Rust core (iroh network stack) links these system libraries. The
+			// Xcode app target must add the same frameworks under "Link Binary With
+			// Libraries" (SystemConfiguration, Security, libresolv).
+			linkerSettings: [
+				.linkedFramework("SystemConfiguration"),
+				.linkedFramework("Security"),
+				.linkedLibrary("resolv"),
+			]
+		),
+		.testTarget(
+			name: "VniDropAppTests",
+			dependencies: ["VniDropApp"],
+			path: "Tests"
+		),
+	]
+)