[iOS] In-app volume controls the device ringer volume instead of media volume

Can reproduce CR; media volume only gets used when a video or sound is already playing rather than the expected behavior even without. Version 1.0.0, Beta 63, Channel Beta, Build 70, iOS 26.6.1 (arm64), Device iPhone17,4, Locale en-US, Push apns, Flutter 3.47.3, Dart 3.13.3