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>

packages/vitec/Configuration/TypoScript/Headless/vitec_news.typoscript

@@ -0,0 +1,30 @@
+# =============================================================================
+# VITEC news integration — headless JSON output
+#
+# All supported EXT:news content element types use the same JSON renderer.
+# The renderer returns a stable payload with:
+#   - mode = list | detail
+#   - items/news = serialised records
+#   - settings = the relevant FlexForm settings for the frontend
+# =============================================================================
+
+tt_content.news_pi1 =< lib.contentElementWithHeader
+tt_content.news_pi1 {
+    fields {
+        content {
+            fields {
+                news = USER
+                news.userFunc = Evomedien\Vitec\UserFunc\NewsJsonRenderer->render
+            }
+        }
+    }
+}
+
+tt_content.news_newsliststicky < tt_content.news_pi1
+tt_content.news_newsselectedlist < tt_content.news_pi1
+tt_content.news_newsdetail < tt_content.news_pi1
+tt_content.news_newsdatemenu < tt_content.news_pi1
+tt_content.news_categorylist < tt_content.news_pi1
+tt_content.news_newssearchform < tt_content.news_pi1
+tt_content.news_newssearchresult < tt_content.news_pi1
+tt_content.news_taglist < tt_content.news_pi1