chore: retire legacy custom CMS (content-editor.js) (MITHOME-93)

Removes the standalone, git-push-based content editor that predates
Payload CMS: content-editor.js, its scripts/cms-*.js modules, its
scripts/test-content-editor-*.js + scripts/test-cms-publish.js test
suite, scripts/markdown-render.js (only used by the editor's guide
renderer), the proto-side test doubles (cms-editor-client.test.ts,
cms-editor-shortcuts.test.ts), and the editor's own user guide
(docs/felhasznaloi-utmutato.md).

Kept: proto/src/content/*.json (still the source for
migrate-content-to-payload.ts and test fixtures for Header/Footer,
per MITHOME-96), proto/src/content/schema.js + scripts/test-content-schema.js
(still validate those JSON files), and docs/content-editor-recovery.md
(historical incident record, not user-facing tool docs).

Safety net before deletion (per user request): added
proto/scripts/export-content-snapshot.ts, a reusable Payload Local API
exporter, and ran it to produce docs/backups/payload-content-snapshot-*.json
— a full hu/en snapshot of every Global + LegalPages + Partners document
at the moment of retirement. Also confirmed no data-loss risk otherwise:
.content-backups/ (the editor's own gitignored backup dir) tops out at
2026-08-23, well before today's fresh migration run, and every JSON
edit ever made through the editor already exists as its own git commit
("content: frissítve a CMS-ből").

Updated dangling references: pre-deploy-tests.sh and
.agent/steering/testing.md (dropped the CMS test block),
.agent/workflows/deploy.md (publish flow is now Payload draft/publish,
not git push), CLAUDE.md + .agent/AGENTS.md (dropped the /cms-feature
workflow, deleted alongside it), README.md (stack description),
.agent/steering/development-rules.md (the guide-maintenance rule no
longer has a guide to maintain).

Verified: tsc, lint, proto unit tests (51 passed), root
test-content-schema.js, plane-sync unit tests, production build all
green after the deletion.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -5,10 +5,10 @@ Modern Next.js weboldal a mozdIT Bt. számára — webtárhely, email- és DNS-s
 ## Stack
 
 - **Frontend**: Next.js 15 (Turbopack), React 19, TypeScript, Tailwind CSS 4
-- **Tartalom**: JSON-alapú, séma-validált content rendszer (`proto/src/content/`)
-- **CMS**: saját, dependency-mentes `content-editor.js` (böngészős szerkesztő)
+- **CMS**: Payload CMS (self-hosted, `/admin`), MongoDB adapter, draft/publish + verziózás, hu/en lokalizáció
+- **Tartalom**: Payload Globals/Collections (a korábbi JSON-alapú content rendszer, `proto/src/content/`, csak a migrációs script forrásaként és teszt-fixture-ként él tovább — MITHOME-91/93)
 - **Backend**: Next.js API routes, MongoDB
-- **Tesztelés**: Jest, React Testing Library, Playwright (smoke), valódi szervert indító CMS-tesztek
+- **Tesztelés**: Jest, React Testing Library, Playwright (smoke)
 - **Deploy**: natív Docker Compose (`deploy.sh`) + Gitea Actions nélkül, lokálisan vezérelt
 - **Monitoring**: Winston + Loki, plusz `scripts/security-scan.sh` (ntfy riasztással)