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/VnidropCore/Package.swift

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+// swift-tools-version:5.9
+import PackageDescription
+
+// Local package wrapping the VniDrop Rust core:
+//   - `vnidrop` binary target: the xcframework of static libraries + the FFI
+//     C module (`vnidropFFI`), produced by apple/scripts/build-core.sh.
+//   - `VnidropCore` target: the generated Swift bindings (`Vnidrop.swift`).
+//
+// Both `vnidrop.xcframework` and `Sources/VnidropCore/Vnidrop.swift` are build
+// outputs and are gitignored; run apple/scripts/build-core.sh to (re)generate.
+let package = Package(
+	name: "VnidropCore",
+	platforms: [
+		.iOS(.v16),
+		.macOS(.v13),
+	],
+	products: [
+		.library(name: "VnidropCore", targets: ["VnidropCore"]),
+	],
+	targets: [
+		.binaryTarget(
+			name: "vnidrop",
+			path: "vnidrop.xcframework"
+		),
+		.target(
+			name: "VnidropCore",
+			dependencies: ["vnidrop"]
+		),
+	]
+)

apple/VnidropCore/README.md

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+# VnidropCore (Swift package)
+
+Swift bindings for the VniDrop Rust transfer core (`crates/vnidrop`), generated
+with UniFFI in library mode. The Rust crate is never modified for this — the
+Swift surface is produced from the compiled staticlib.
+
+## Regenerate
+
+From the repository root:
+
+```bash
+apple/scripts/build-core.sh release   # or: debug
+```
+
+This builds `libvnidrop.a` for `aarch64-apple-ios`, `aarch64-apple-ios-sim`, and
+`aarch64-apple-darwin`, generates `Sources/VnidropCore/Vnidrop.swift`, and
+assembles `vnidrop.xcframework`.
+
+## Generated / ignored artifacts
+
+- `vnidrop.xcframework/`
+- `Sources/VnidropCore/Vnidrop.swift`
+
+Both are gitignored. A clean checkout must run the build script before opening
+the Xcode project.