GitHub only runs workflows from .github/workflows at the root, so the six
workflows inherited from the two projects have to live there rather than under
web/ and android/. Each one gets a path filter so web-only changes do not
trigger Android builds, a working directory for its subproject, and a prefixed
filename to keep the two sets apart.
Gradle now sits at android/android, the Firebase action reads its config from
web/ via entryPoint, and the Android checkout no longer needs submodules.
