Add iOS app with CarPlay and Siri

SwiftUI port of the Android app under ios/, with CarPlay browse and
Now Playing, Siri play-media intents, and a build-ipa.sh script that
makes an unsigned IPA for sideloading. README gets an iOS section and
the vibecoded disclaimer.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

ios/Stemify/UI/Theme.swift

@@ -0,0 +1,80 @@
+import SwiftUI
+
+extension Color {
+    init(hex: UInt32, alpha: Double = 1) {
+        self.init(.sRGB, red: Double((hex >> 16) & 0xFF) / 255, green: Double((hex >> 8) & 0xFF) / 255,
+                  blue: Double(hex & 0xFF) / 255, opacity: alpha)
+    }
+}
+
+/// The three themes' colours. Black is true black for OLED; no gradients anywhere.
+struct Palette {
+    var dark: Bool
+    var bg: Color
+    var groupedBg: Color
+    var cell: Color
+    var fill: Color
+    var fillStrong: Color
+    var label: Color
+    var label2: Color
+    var label3: Color
+    var separator: Color
+    var placeholder: Color
+    var accent: Color
+    var red: Color
+
+    static func of(_ mode: ThemeMode, _ accent: Accent) -> Palette {
+        switch mode {
+        case .Black:
+            Palette(dark: true, bg: Color(hex: 0x000000), groupedBg: Color(hex: 0x000000), cell: Color(hex: 0x1C1C1E),
+                    fill: Color(hex: 0x1C1C1E), fillStrong: Color(hex: 0x3A3A3C), label: .white, label2: Color(hex: 0x8D8D93),
+                    label3: Color(hex: 0x48484A), separator: Color(hex: 0x2C2C2E), placeholder: Color(hex: 0x1C1C1E),
+                    accent: Color(hex: accent.dark), red: Color(hex: 0xFF453A))
+        case .Dark:
+            Palette(dark: true, bg: Color(hex: 0x1C1C1E), groupedBg: Color(hex: 0x1C1C1E), cell: Color(hex: 0x2C2C2E),
+                    fill: Color(hex: 0x2C2C2E), fillStrong: Color(hex: 0x48484A), label: .white, label2: Color(hex: 0x98989D),
+                    label3: Color(hex: 0x5A5A5E), separator: Color(hex: 0x3D3D40), placeholder: Color(hex: 0x3A3A3C),
+                    accent: Color(hex: accent.dark), red: Color(hex: 0xFF453A))
+        case .White:
+            Palette(dark: false, bg: Color(hex: 0xFFFFFF), groupedBg: Color(hex: 0xF2F2F7), cell: Color(hex: 0xFFFFFF),
+                    fill: Color(hex: 0xEFEFF0), fillStrong: Color(hex: 0xE3E3E8), label: .black, label2: Color(hex: 0x8A8A8E),
+                    label3: Color(hex: 0xC4C4C7), separator: Color(hex: 0xD8D8DC), placeholder: Color(hex: 0xE5E5EA),
+                    accent: Color(hex: accent.light), red: Color(hex: 0xFF3B30))
+        }
+    }
+}
+
+private struct PaletteKey: EnvironmentKey {
+    static let defaultValue = Palette.of(.Black, .Music)
+}
+
+extension EnvironmentValues {
+    var palette: Palette {
+        get { self[PaletteKey.self] }
+        set { self[PaletteKey.self] = newValue }
+    }
+}
+
+extension View {
+    /// A list on the theme's background instead of the system one.
+    func themedList(grouped: Bool = true) -> some View { modifier(ThemedList(grouped: grouped)) }
+
+    /// Rows on the theme's cell colour.
+    func themedRow(grouped: Bool = true) -> some View { modifier(ThemedRow(grouped: grouped)) }
+}
+
+private struct ThemedList: ViewModifier {
+    @Environment(\.palette) private var p
+    let grouped: Bool
+    func body(content: Content) -> some View {
+        content.scrollContentBackground(.hidden).background(grouped ? p.groupedBg : p.bg)
+    }
+}
+
+private struct ThemedRow: ViewModifier {
+    @Environment(\.palette) private var p
+    let grouped: Bool
+    func body(content: Content) -> some View {
+        content.listRowBackground(grouped ? p.cell : p.bg).listRowSeparatorTint(p.separator)
+    }
+}