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/CarPlay/HomeReach.swift

@@ -0,0 +1,73 @@
+import Foundation
+import Observation
+
+/// Whether Plex or stemserve answers right now. In the car the phone is usually on cellular
+/// and the LAN addresses just time out, so the car UI asks this first (a quick probe,
+/// remembered briefly) and goes straight to cached data when home is out of reach.
+@Observable
+final class HomeReach: @unchecked Sendable {
+    private static let ttl: UInt64 = 20_000_000_000
+
+    @ObservationIgnored private let settings: Settings
+    @ObservationIgnored private let session: URLSession
+    @ObservationIgnored private let lock = AsyncLock()
+    @ObservationIgnored private let stamp = UnfairLock()
+    @ObservationIgnored private var checkedAt: UInt64 = 0
+    @ObservationIgnored private var _last = true
+    @ObservationIgnored private var listeners: [() -> Void] = []
+
+    /// The last answer; true until a probe says otherwise. Changes as the phone joins or leaves home Wi-Fi.
+    private(set) var home = true
+
+    /// Readable from any thread (the car's Plex client asks it on every request).
+    var lastKnown: Bool { stamp.with { _last } }
+
+    init(settings: Settings, net: Connectivity) {
+        self.settings = settings
+        let c = URLSessionConfiguration.ephemeral
+        c.timeoutIntervalForRequest = 2
+        c.timeoutIntervalForResource = 2.5
+        c.waitsForConnectivity = false
+        session = URLSession(configuration: c)
+        // A new network (home Wi-Fi in range, or lost) invalidates the answer; ask again once it
+        // settles, so the car's lists can switch over without anyone browsing first.
+        net.onChange { [weak self] in
+            guard let self else { return }
+            self.stamp.with { self.checkedAt = 0 }
+            Task {
+                try? await Task.sleep(nanoseconds: 1_500_000_000)
+                _ = await self.reachable()
+            }
+        }
+    }
+
+    /// Main-thread callback when [home] changes.
+    func onChange(_ f: @escaping () -> Void) { listeners.append(f) }
+
+    func reachable() async -> Bool {
+        await lock.run {
+            let now = DispatchTime.now().uptimeNanoseconds
+            let (at, last) = stamp.with { (checkedAt, _last) }
+            if at != 0 && now - at < Self.ttl { return last }
+            let plex = settings.plexUrl.trimmingCharacters(in: CharacterSet(charactersIn: "/")) + "/identity"
+            let stems = settings.stemUrl.trimmingCharacters(in: CharacterSet(charactersIn: "/")) + "/api/info"
+            async let a = answers(plex)
+            async let b = answers(stems)
+            let (ra, rb) = await (a, b)
+            let ok = ra || rb
+            stamp.with { _last = ok; checkedAt = DispatchTime.now().uptimeNanoseconds }
+            await MainActor.run {
+                if home != ok {
+                    home = ok
+                    listeners.forEach { $0() }
+                }
+            }
+            return ok
+        }
+    }
+
+    private func answers(_ s: String) async -> Bool {
+        guard let url = URL(string: s), let (_, r) = try? await session.data(from: url) else { return false }
+        return ((r as? HTTPURLResponse)?.statusCode ?? 500) < 500
+    }
+}