The registry: coords_hud, the checks, publishing to Pages, the weekly cleanup

- mods/coords_hud.toml: the SDK's example mod, MIT, built from
  crates/horizon-mod-sdk/examples/coords-hud in Horizon.
- check.yml: a pull request's changes, each new file's checks and a trial
  run in the sandbox, the index it would publish (cargo horizon-mod from
  Horizon at HORIZON_REV).
- publish.yml: on main, new versions become releases, index.json and the
  icons go to GitHub Pages.
- cleanup.yml: staging copies nobody needs, weekly.
- CODEOWNERS, the report form, the pull request template, revoked.toml.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.github/CODEOWNERS

@@ -0,0 +1,5 @@
+# Every change needs a review from one of these before it merges (branch protection:
+# "Require review from Code Owners"). Add trusted contributors to the first line.
+*            @ludovic111 @rdbtCVS @levzzz5154 @socksprox
+/.github/    @ludovic111
+/revoked.toml @ludovic111