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>

.gitignore

@@ -16,3 +16,9 @@ android/captures/
 # Built and third-party APKs (publish builds as GitHub Releases instead)
 *.apk
 *.aab
+
+# iOS
+ios/build/
+ios/Stemify.xcodeproj/
+ios/Stemify/Info.plist
+ios/Stemify/Stemify.entitlements