Embed the publish script in .gitea/scoped_workflows/publish-wiki.yml and
remove the repository workflow and tools/publish_wiki.py. A repository
publishes only when wiki/.publish exists; the word prune in it is the only
thing that lets the workflow delete pages. The organisation's
TOKEN_FOR_GITEA_WIKI is used with no fallback. This repository opts in with
prune. Tests run the embedded script against a fake Gitea.
Task: MIL-006#2
Task: MIL-006#3
