mirror/github-mirror.sh publishes main and its tags to a read-only
GitHub mirror, adding a notice under the README title, with a systemd
timer to run it hourly. A GitHub Actions workflow builds the images on
the mirror and pushes them to ghcr.io. The docs point prebuilt images
there, and CONTRIBUTING no longer invites issues and pull requests.
upstream-status.sh now fetches without tags, so upstream's version tags
stay out of local clones.
Adds scripts/upstream-status.sh to report upstream flashpoint-web changes
since the last merge, docs/08-development/upstream-sync.md describing the
merge process, and .dejima.md for agents working in dejima.
branderson