[Long-term] Custom wake word (.tflite) support in Android Companion app

Companion the maintainer comment on issue #6472: "this might come later, from a contribution, for now I'm focusing on getting the best of what we have." Tracking to know when first-party support lands.

In the meantime, workarounds in the issue thread (APK injection via #6472 comments, Termux + wyoming-satellite-termux) let users run custom wake words today.

Upstream issue: https://github.com/home-assistant/android/issues/6472

Start with upstream issue #6472 and review its comments, including the documented APK-injection and Termux workarounds. Done means first-party support for custom .tflite wake words in the Android Companion app; this issue names no source file or test to begin with.

Written by the indexing model from the issue text.