Neutralize internal-host references for publication

The CI workflow comment named the internal server, and
PLUGIN-EXTERNAL-REPO carried internal gitea clone URLs (it becomes a
public wiki page). Point both at the GitHub home / a generic CI
mention so the publication scrub gate passes and the wiki does not
expose internal infrastructure.

.github/workflows/ci.yml

@@ -1,6 +1,6 @@
 # CI for shopdb-flask on GitHub Actions.
 #
-# Mirrors the internal gitea pipeline. Four jobs on push + pull_request:
+# Mirrors the internal CI pipeline. Four jobs on push + pull_request:
 #   backend          - pytest (SQLite via TestingConfig, no DB service needed)
 #   naming           - the CONTRIBUTING.md naming/style gate
 #   frontend         - vitest + Vue build