cms: add openbureau-core CMS (DB-less, auth: local) — vendored at cms/core

kgva can now be edited through openbureau-core instead of Decap: a small Node CMS
(git subtree at cms/core) with a schema-driven editor at /admin, file-based login
(no Supabase/Postgres), Markdown on disk. cms/kgva.config.js models the content
(portfolio/pages/sections); docker-compose builds the core image (Hugo 0.163.3,
no VITE_SUPABASE_URL → local-auth admin) and mounts the repo as the site. seed an
admin via cms/seed-admin.mjs; deploy/provision-lxc.sh + ADMIN.md updated.

Verified DB-less end-to-end on real content (staged): local login → schema-driven
editor → 42 entries (de/en) → stats → create/preview/cleanup; unknown frontmatter
(image galleries) preserved on save. The LIVE static site (CT130 timer→hugo→nginx)
is unaffected — hugo ignores cms/; the CMS is dormant until provisioned.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,6 @@
+
+# CMS (db-less) secrets + users + build
+cms/.env
+cms/users.json
+public/
+resources/