Call for testers: run the app on real hardware

[HMAKT99]

The whole pipeline is unit-tested (88 JVM tests) and verified on the Android 15 emulator, but no audio has ever run on a real phone with real earbuds. This is the #1 thing blocking a stable release.

If you have an Android phone + any earbuds (wired or Bluetooth):

1. Install the latest alpha.
2. Follow docs/DEVICE_TESTING.md.
3. Report here: device model, Android version, earbud model, wired/BT, and especially latency feel (echo?) and any feedback/howling.

⚠️ Start with LOW amplification and the comfort ceiling at default. Not a medical device.