Use a reverse-domain redirect scheme for the native app

- Android/iOS now return to cat.ikerdemo.musify:/callback instead of
  musify://callback: a private-use scheme based on a domain we own
  (RFC 8252 section 7.1), so another app is unlikely to claim it.
- The Musify Native app no longer needs devMode: loopback and custom
  scheme redirects are both valid for a native app.
- zitadel-init also updates an existing app's config, so the change
  reaches instances created before it (the client id is kept).
- iOS takes the scheme from everything before the first ':', since the
  new URI has a single slash.

mobile/composeApp/src/iosMain/kotlin/com/musify/app/Config.ios.kt

@@ -12,5 +12,5 @@ actual object AppConfig {
 
     // Matches CFBundleURLTypes in Info.plist and the redirect URI registered
     // for the "Musify Native" app in Zitadel.
-    actual val nativeRedirectUri: String = "musify://callback"
+    actual val nativeRedirectUri: String = "cat.ikerdemo.musify:/callback"
 }

mobile/composeApp/src/iosMain/kotlin/com/musify/app/auth/BrowserAuthLauncher.ios.kt

@@ -23,14 +23,15 @@ private class PresentationContextProvider : NSObject(), ASWebAuthenticationPrese
 /**
  * `ASWebAuthenticationSession` owns the whole round trip: it opens a system
  * browser sheet at [authorizeUrl] (Zitadel's hosted login, with its
- * "Regístrate" link) and intercepts the `musify://` redirect itself, no app
+ * "Regístrate" link) and intercepts the `cat.ikerdemo.musify:` redirect itself, no app
  * delegate / `onOpenURL` wiring required.
  */
 @OptIn(ExperimentalForeignApi::class)
 actual class BrowserAuthLauncher actual constructor() {
     actual suspend fun launch(authorizeUrl: String, redirectUri: String): String =
         suspendCancellableCoroutine { continuation ->
-            val scheme = redirectUri.substringBefore("://")
+            // `scheme:/path` (RFC 8252 private-use scheme): everything before the first ':'.
+            val scheme = redirectUri.substringBefore(":")
             val contextProvider = PresentationContextProvider()
 
             val session = ASWebAuthenticationSession(