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>

CLAUDE.md

@@ -59,7 +59,7 @@ websitedev/
 ├── .agent/                     # AI szabályrendszer ← OLVASD EL
 │   ├── AGENTS.md               # Elsődleges szabályok
 │   ├── steering/               # Auto-betöltődő irányelvek
-│   ├── workflows/              # /new-feature, /fix-bug, /cms-feature, /review, /deploy
+│   ├── workflows/              # /new-feature, /fix-bug, /review, /deploy
 │   └── references/             # Accessibility checklist
 ├── TODO.md                     # Feladatlista (Plane szinkron)
 └── plane-sync.js               # Plane szinkronizáló script
@@ -98,7 +98,6 @@ Szükséges változók (`.env` és `proto/.env.local`):
 | `.agent/steering/testing.md` | Tesztelési stratégia, coverage elvárások |
 | `.agent/workflows/new-feature.md` | Új funkció fejlesztési lépései |
 | `.agent/workflows/fix-bug.md` | Hibajavítás lépései (TDD) |
-| `.agent/workflows/cms-feature.md` | CMS fejlesztés + útmutató karbantartás |
 | `.agent/workflows/review.md` | Code review checklist |
 | `.agent/workflows/deploy.md` | Deployment folyamat |
 | `.agent/references/accessibility-checklist.md` | WCAG 2.1 AA ellenőrzőlista |