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/project.yml

@@ -0,0 +1,46 @@
+# XcodeGen spec for the native SwiftUI VniDrop app (iOS/iPadOS/macOS).
+# Regenerate the project with:  xcodegen generate  (run from apple/)
+# Requires the Rust core first:  apple/scripts/build-core.sh debug
+name: VniDrop
+options:
+  bundleIdPrefix: com.vnidrop
+  deploymentTarget:
+    iOS: "18.2"
+    macOS: "15.0"
+  createIntermediateGroups: true
+
+packages:
+  VnidropCore:
+    path: VnidropCore
+
+targets:
+  VniDrop:
+    type: application
+    supportedDestinations: [iOS, macOS]
+    sources:
+      - path: VniDrop
+        excludes:
+          - "Resources/Info.plist"
+          - "Resources/VniDrop.entitlements"
+          - "Resources/**/.DS_Store"
+    settings:
+      base:
+        PRODUCT_BUNDLE_IDENTIFIER: com.vnidrop.app
+        MARKETING_VERSION: "0.1.0"
+        CURRENT_PROJECT_VERSION: "1"
+        GENERATE_INFOPLIST_FILE: NO
+        INFOPLIST_FILE: VniDrop/Resources/Info.plist
+        SWIFT_VERSION: "5.9"
+        ENABLE_USER_SCRIPT_SANDBOXING: NO
+        ASSETCATALOG_COMPILER_APPICON_NAME: AppIcon
+        CODE_SIGN_STYLE: Automatic
+      configs:
+        debug:
+          CODE_SIGN_ENTITLEMENTS: VniDrop/Resources/VniDrop.entitlements
+        release:
+          CODE_SIGN_ENTITLEMENTS: VniDrop/Resources/VniDrop.entitlements
+    dependencies:
+      - package: VnidropCore
+      - sdk: SystemConfiguration.framework
+      - sdk: Security.framework
+      - sdk: libresolv.tbd