- README: render the Key links as real Markdown links (mailto: for the
contact address); drop the 'lives in a public git repository' note now
that the footer carries the source link.
- mkdocs.yml: add a theme override (custom_dir: overrides) that puts a
'Documentation source' link in the footer of every page.
- Move the operator runbook, maintenance notes and incident write-up out
of the published site into the git-only co-op/ops-docs repository;
remove them from the nav and repoint cross-references at Gitea.
