Add evo_megamenu_json extension and seed the megamenu

- new project-neutral extension evo_megamenu_json (Evomedien): a Megamenu
  plugin holding entries, columns, items, teaser cards and a featured slot
  as nested records; presentation settings travel with the payload so the
  front end reads behaviour instead of hard-coding it; published as
  page.10.fields.megaMenu, driven by the site settings megamenu.contentUid
  and megamenu.storagePid
- vitec:seed-megamenu fills one element from the live structure: 5 entries,
  26 columns, 95 items, 4 story cards; items without a page yet are flagged
  pending so the front end falls back to the column link
- vitec:debug-sets prints the resolved site set order
- read-only diagnostics: check_megamenu_schema.php, check_typoscript_templates.php
- docs: schema updates run via extension:setup (database:updateschema no
  longer exists in v14), and a JSON Accept header activates headless-mixed,
  which strips every set-added page field

composer.json

@@ -18,6 +18,7 @@
 		"apache-solr-for-typo3/solr": "^14.0@RC",
 		"b13/container": "^3.1",
 		"b13/typo3-updater": "^1.1",
+		"evomedien/evo-megamenu-json": "^1.0.0",
 		"evomedien/vitec": "^1.0.1",
 		"friendsoftypo3/content-blocks": "^2.4",
 		"friendsoftypo3/headless": "^5.0@rc",