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/androidMain/kotlin/com/musify/app/Config.android.kt

@@ -9,5 +9,5 @@ actual object AppConfig {
 
     // Matches the AuthCallbackActivity intent-filter in AndroidManifest.xml 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"
 }