CI drops the Android client here on every image build, and the Dockerfile copies
the directory into the image (see ci.yml "Fetch the Android client to bake in").

This file exists so the directory does too. `COPY client/ ...` fails outright on a
missing source, which would break every local `docker build` on a tree that has
never run that CI step — and an image with no Android client is a supported
state, not an error.

The artifacts themselves are gitignored: a 55 MiB binary does not belong in git
history, and it is fetched fresh anyway.