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/Cache/ArtLoader.swift

@@ -0,0 +1,48 @@
+import Foundation
+import UIKit
+
+/// Album art: a memory cache over a big disk URLCache, so downloaded albums keep their covers
+/// offline. Stands in for Coil on Android.
+final class ArtLoader: @unchecked Sendable {
+    static let shared = ArtLoader()
+
+    private let memory = NSCache<NSURL, UIImage>()
+    private let session: URLSession
+    private let lock = NSLock()
+    private var inflight: [URL: Task<UIImage?, Never>] = [:]
+
+    init() {
+        let dir = FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask)[0].appendingPathComponent("art", isDirectory: true)
+        let cfg = URLSessionConfiguration.default
+        cfg.urlCache = URLCache(memoryCapacity: 16 << 20, diskCapacity: 512 << 20, directory: dir)
+        cfg.requestCachePolicy = .returnCacheDataElseLoad
+        cfg.timeoutIntervalForRequest = 20
+        session = URLSession(configuration: cfg)
+        memory.totalCostLimit = 64 << 20
+    }
+
+    func cached(_ url: URL) -> UIImage? { memory.object(forKey: url as NSURL) }
+
+    func image(_ url: URL) async -> UIImage? {
+        if let img = cached(url) { return img }
+        if let t = lock.withLock({ inflight[url] }) { return await t.value }
+        let t = Task<UIImage?, Never> { [session] in
+            guard let (data, resp) = try? await session.data(from: url),
+                  (resp as? HTTPURLResponse).map({ (200..<300).contains($0.statusCode) }) ?? true,
+                  let img = UIImage(data: data) else { return nil }
+            let decoded = await img.byPreparingForDisplay() ?? img
+            return decoded
+        }
+        lock.withLock { inflight[url] = t }
+        let img = await t.value
+        lock.withLock { inflight[url] = nil }
+        if let img {
+            memory.setObject(img, forKey: url as NSURL, cost: Int(img.size.width * img.size.height * img.scale * img.scale * 4))
+        }
+        return img
+    }
+
+    func prefetch(_ url: URL) {
+        Task.detached(priority: .utility) { _ = await self.image(url) }
+    }
+}