Checkpoint: headless JSON architecture documented + cleanup (Stufe 1+2)

Restore point before Stufe 3 (central resolver-service refactoring).

Includes this session's work:
- Success Story (usecase) rebuild: new fields/tabs, UsecaseSerializer,
  thin List/Show renderers, MM relations, inline content elements.
- vitec_columns content block (two-column layout with per-item content)
  incl. unified header section; special-cased JSON resolution.
- Container per-column flex (items[].config align/justify) + gap on parent.
- Unified header section across CEs/plugins/containers; header fields in JSON.
- ISO-style architecture spec: Documentation/Headless-JSON-Architecture.md.
- Cleanup: removed local scratch + verified .bak backups.
- Fixes: B-6 (undefined thumbnail variable in Downloadcardcollection image
  resolver), B-7 (unsatisfiable legacy CType OR branch in Downloadcard/Datasheets).

Rollback: git reset --hard snapshot-2026-07-09-pre-stufe3

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

composer.json

@@ -20,6 +20,7 @@
 		"evomedien/vitec": "^1.0.1",
 		"friendsoftypo3/content-blocks": "^2.4",
 		"friendsoftypo3/headless": "^5.0@rc",
+		"georgringer/news": "^14.0",
 		"netzbewegung/nb-headless-content-blocks": "^0.0.23",
 		"typo3/cms-backend": "^14.3",
 		"typo3/cms-belog": "^14.3",