Add auto-generated project-tree snapshots for the website, link, and
Android-app repos under docs/<repo>/PROJECT_TREE.md, and link them from
the README (adding a previously-missing android/ section). These files
are maintained going forward by the sync-project-tree CI workflow in each
source repo, which opens a PR here whenever the tracked layout changes.
Co-Authored-By: Claude <noreply@anthropic.com>
