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/UI/Theme/Typography.swift

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+import SwiftUI
+
+/// Semantic type scale mapped from the Material typography styles the Compose UI
+/// uses, so screens reference the same names during the port.
+enum VniType {
+	static let titleLarge = Font.system(size: 22, weight: .semibold)
+	static let bodyLarge = Font.system(size: 16)
+	static let bodyMedium = Font.system(size: 14)
+	static let bodySmall = Font.system(size: 12)
+	static let labelSmall = Font.system(size: 11, weight: .medium)
+}

apple/VniDrop/UI/Theme/VniDropColors.swift

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+import SwiftUI
+
+/// Direct Compose port of the VniDrop semantic color tokens
+/// (`shared/.../ui/theme/VniDropTheme.kt`). The app uses these semantic tokens
+/// directly because a single SwiftUI/Material color scheme cannot represent the
+/// full surface, border, and foreground stack.
+struct VniDropColors {
+	let backgroundDefault: Color
+	let backgroundDashCanvas: Color
+	let backgroundDashSidebar: Color
+	let backgroundSurface75: Color
+	let backgroundSurface100: Color
+	let backgroundSurface200: Color
+	let backgroundSurface300: Color
+	let backgroundSurface400: Color
+	let backgroundMuted: Color
+	let backgroundControl: Color
+	let backgroundSelection: Color
+	let backgroundButton: Color
+	let backgroundOverlayHover: Color
+	let backgroundDialog: Color
+	let borderDefault: Color
+	let borderStrong: Color
+	let borderStronger: Color
+	let borderMuted: Color
+	let borderControl: Color
+	let foregroundDefault: Color
+	let foregroundLight: Color
+	let foregroundLighter: Color
+	let foregroundMuted: Color
+	let foregroundContrast: Color
+	let brandLink: Color
+	let brandButton: Color
+	let brandDefault: Color
+	let brand600: Color
+	let brand500: Color
+	let brand400: Color
+	let brand300: Color
+	let brand200: Color
+	let warningDefault: Color
+	let warning200: Color
+	let warning300: Color
+	let warning400: Color
+	let warning500: Color
+	let warning600: Color
+	let destructiveDefault: Color
+	let destructive200: Color
+	let destructive300: Color
+	let destructive400: Color
+	let destructive500: Color
+	let destructive600: Color
+}
+
+extension VniDropColors {
+	/// The single brand accent used app-wide as the SwiftUI tint.
+	static let brandPurple = Color.hsl(271, 91, 65)
+
+	static let light = VniDropColors(
+		backgroundDefault: .hsl(0, 0, 98.8),
+		backgroundDashCanvas: .hsl(0, 0, 97.3),
+		backgroundDashSidebar: .hsl(0, 0, 98.8),
+		backgroundSurface75: .hsl(0, 0, 100),
+		backgroundSurface100: .hsl(0, 0, 98.8),
+		backgroundSurface200: .hsl(0, 0, 95.3),
+		backgroundSurface300: .hsl(0, 0, 92.9),
+		backgroundSurface400: .hsl(0, 0, 89.8),
+		backgroundMuted: .hsl(0, 0, 96.9),
+		backgroundControl: .hsl(0, 0, 95.3),
+		backgroundSelection: .hsl(0, 0, 92.9),
+		backgroundButton: .hsl(0, 0, 91),
+		backgroundOverlayHover: .hsl(0, 0, 95.3),
+		backgroundDialog: .hsl(0, 0, 100),
+		borderDefault: .hsl(0, 0, 87.5),
+		borderStrong: .hsl(0, 0, 83.1),
+		borderStronger: .hsl(0, 0, 56.1),
+		borderMuted: .hsl(0, 0, 92.9),
+		borderControl: .hsl(0, 0, 78),
+		foregroundDefault: .hsl(0, 0, 9),
+		foregroundLight: .hsl(0, 0, 32.2),
+		foregroundLighter: .hsl(0, 0, 43.9),
+		foregroundMuted: .hsl(0, 0, 69.8),
+		foregroundContrast: .hsl(0, 0, 98.4),
+		brandLink: .hsl(271, 91, 65),
+		brandButton: .hsl(270, 95, 75),
+		brandDefault: .hsl(271, 91, 65),
+		brand600: .hsl(271, 81, 56),
+		brand500: .hsl(271, 91, 65),
+		brand400: .hsl(270, 95, 75),
+		brand300: .hsl(269, 97, 85),
+		brand200: .hsl(269, 100, 92),
+		warningDefault: .hsl(38.9, 100, 57.1),
+		warning200: .hsl(40, 81.8, 97.8),
+		warning300: .hsl(44.3, 100, 91.8),
+		warning400: .hsl(41.9, 100, 81.8),
+		warning500: .hsl(36.3, 85.7, 67.1),
+		warning600: .hsl(30.3, 80.3, 47.8),
+		destructiveDefault: .hsl(10.2, 77.9, 53.9),
+		destructive200: .hsl(0, 100, 99.4),
+		destructive300: .hsl(7.1, 100, 96.7),
+		destructive400: .hsl(7.1, 91.3, 91),
+		destructive500: .hsl(10.4, 77.1, 79.4),
+		destructive600: .hsl(9.9, 82, 43.5)
+	)
+
+	static let dark = VniDropColors(
+		backgroundDefault: .hsl(0, 0, 7.1),
+		backgroundDashCanvas: .hsl(0, 0, 7.1),
+		backgroundDashSidebar: .hsl(0, 0, 9),
+		backgroundSurface75: .hsl(0, 0, 9),
+		backgroundSurface100: .hsl(0, 0, 12.2),
+		backgroundSurface200: .hsl(0, 0, 12.9),
+		backgroundSurface300: .hsl(0, 0, 16.1),
+		backgroundSurface400: .hsl(0, 0, 16.1),
+		backgroundMuted: .hsl(0, 0, 14.1),
+		backgroundControl: .hsl(0, 0, 14.1),
+		backgroundSelection: .hsl(0, 0, 19.2),
+		backgroundButton: .hsl(0, 0, 18),
+		backgroundOverlayHover: .hsl(0, 0, 18),
+		backgroundDialog: .hsl(0, 0, 7.1),
+		borderDefault: .hsl(0, 0, 18),
+		borderStrong: .hsl(0, 0, 21.2),
+		borderStronger: .hsl(0, 0, 27.1),
+		borderMuted: .hsl(0, 0, 14.1),
+		borderControl: .hsl(0, 0, 22.4),
+		foregroundDefault: .hsl(0, 0, 98),
+		foregroundLight: .hsl(0, 0, 70.6),
+		foregroundLighter: .hsl(0, 0, 53.7),
+		foregroundMuted: .hsl(0, 0, 30.2),
+		foregroundContrast: .hsl(0, 0, 8.6),
+		brandLink: .hsl(270, 95, 75),
+		brandButton: .hsl(271, 81, 56),
+		brandDefault: .hsl(270, 95, 75),
+		brand600: .hsl(271, 91, 65),
+		brand500: .hsl(271, 81, 56),
+		brand400: .hsl(273, 67, 39),
+		brand300: .hsl(274, 66, 32),
+		brand200: .hsl(274, 87, 21),
+		warningDefault: .hsl(38.9, 100, 42.9),
+		warning200: .hsl(36.6, 100, 8),
+		warning300: .hsl(32.3, 100, 10.2),
+		warning400: .hsl(33.2, 100, 14.5),
+		warning500: .hsl(34.8, 90.9, 21.6),
+		warning600: .hsl(38.9, 100, 42.9),
+		destructiveDefault: .hsl(10.2, 77.9, 53.9),
+		destructive200: .hsl(10.9, 23.4, 9.2),
+		destructive300: .hsl(7.5, 51.3, 15.3),
+		destructive400: .hsl(6.7, 60, 20.6),
+		destructive500: .hsl(7.9, 71.6, 29),
+		destructive600: .hsl(9.7, 85.2, 62.9)
+	)
+}
+
+extension Color {
+	/// HSL constructor matching the Compose `hsl()` helper (hue in degrees,
+	/// saturation and lightness in percent).
+	static func hsl(_ hue: Double, _ saturation: Double, _ lightness: Double) -> Color {
+		let h = (hue.truncatingRemainder(dividingBy: 360) + 360)
+			.truncatingRemainder(dividingBy: 360) / 360
+		let s = min(max(saturation, 0), 100) / 100
+		let l = min(max(lightness, 0), 100) / 100
+		if s == 0 {
+			return Color(red: l, green: l, blue: l)
+		}
+		let q = l < 0.5 ? l * (1 + s) : l + s - l * s
+		let p = 2 * l - q
+		return Color(
+			red: hueToRgb(p, q, h + 1.0 / 3.0),
+			green: hueToRgb(p, q, h),
+			blue: hueToRgb(p, q, h - 1.0 / 3.0)
+		)
+	}
+}
+
+private func hueToRgb(_ p: Double, _ q: Double, _ input: Double) -> Double {
+	var t = input
+	if t < 0 { t += 1 }
+	if t > 1 { t -= 1 }
+	let value: Double
+	if t < 1.0 / 6.0 {
+		value = p + (q - p) * 6 * t
+	} else if t < 1.0 / 2.0 {
+		value = q
+	} else if t < 2.0 / 3.0 {
+		value = p + (q - p) * (2.0 / 3.0 - t) * 6
+	} else {
+		value = p
+	}
+	return min(1, max(0, value))
+}

apple/VniDrop/UI/Theme/VniDropTheme.swift

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+import SwiftUI
+
+/// User-facing theme selection, mirrors `ThemeMode` in the Compose theme.
+enum ThemeMode: String, CaseIterable, Codable, Sendable {
+	case system
+	case light
+	case dark
+
+	/// SwiftUI color-scheme override (`nil` follows the system).
+	var preferredColorScheme: ColorScheme? {
+		switch self {
+		case .system: return nil
+		case .light: return .light
+		case .dark: return .dark
+		}
+	}
+}
+
+func resolveDarkTheme(_ mode: ThemeMode, systemDark: Bool) -> Bool {
+	switch mode {
+	case .system: return systemDark
+	case .light: return false
+	case .dark: return true
+	}
+}
+
+private struct VniDropColorsKey: EnvironmentKey {
+	static let defaultValue = VniDropColors.light
+}
+
+extension EnvironmentValues {
+	/// Semantic VniDrop tokens for the active theme. Read with
+	/// `@Environment(\.vniColors) private var colors`.
+	var vniColors: VniDropColors {
+		get { self[VniDropColorsKey.self] }
+		set { self[VniDropColorsKey.self] = newValue }
+	}
+}
+
+/// Provides the semantic token set matching the resolved light/dark theme to the
+/// whole subtree. Apply once near the app root.
+struct VniDropTheme: ViewModifier {
+	let isDark: Bool
+
+	func body(content: Content) -> some View {
+		content
+			.environment(\.vniColors, isDark ? .dark : .light)
+			.tint(VniDropColors.brandPurple)
+	}
+}
+
+extension View {
+	func vniDropTheme(isDark: Bool) -> some View {
+		modifier(VniDropTheme(isDark: isDark))
+	}
+}