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

packages/evo_megamenu_json/Configuration/TCA/Overrides/tt_content.php

@@ -0,0 +1,64 @@
+<?php
+
+declare(strict_types=1);
+
+defined('TYPO3') or die();
+
+use TYPO3\CMS\Extbase\Utility\ExtensionUtility;
+
+/**
+ * Registers the "Megamenu" plugin (CType evomegamenujson_megamenu).
+ *
+ * The element carries the whole menu: its entries live inline below it, and
+ * the FlexForm holds the presentation settings the front end reads back out
+ * of the JSON (stage, hover behaviour, column count, labels).
+ *
+ * Place ONE element per menu - typically on a sysfolder - and point the site
+ * setting `megamenu.contentUid` at it to expose the menu at page level.
+ */
+(static function (): void {
+    ExtensionUtility::registerPlugin(
+        'EvoMegamenuJson',
+        'Megamenu',
+        'LLL:EXT:evo_megamenu_json/Resources/Private/Language/locallang_db.xlf:plugin.megamenu',
+        'evomegamenujson-plugin',
+        'menu',
+        'LLL:EXT:evo_megamenu_json/Resources/Private/Language/locallang_db.xlf:plugin.megamenu.description',
+        'FILE:EXT:evo_megamenu_json/Configuration/FlexForms/Megamenu.xml'
+    );
+
+    $ll = 'LLL:EXT:evo_megamenu_json/Resources/Private/Language/locallang_db.xlf:';
+
+    $GLOBALS['TCA']['tt_content']['columns']['tx_evomegamenujson_entries'] = [
+        'label' => $ll . 'tt_content.entries',
+        'description' => $ll . 'tt_content.entries.description',
+        'config' => [
+            'type' => 'inline',
+            'foreign_table' => 'tx_evomegamenujson_entry',
+            'foreign_field' => 'parentid',
+            'foreign_table_field' => 'parenttable',
+            'foreign_sortby' => 'sorting',
+            'maxitems' => 12,
+            'appearance' => [
+                'collapseAll' => true,
+                'expandSingle' => true,
+                'useSortable' => true,
+                'newRecordLinkAddTitle' => true,
+                'levelLinksPosition' => 'top',
+            ],
+        ],
+    ];
+
+    $GLOBALS['TCA']['tt_content']['types']['evomegamenujson_megamenu']['showitem'] = '
+        --div--;LLL:EXT:core/Resources/Private/Language/Form/locallang_tabs.xlf:general,
+            --palette--;;general,
+            header,
+        --div--;' . $ll . 'tt_content.tab.entries,
+            tx_evomegamenujson_entries,
+        --div--;LLL:EXT:core/Resources/Private/Language/Form/locallang_tabs.xlf:plugin,
+            pi_flexform,
+        --div--;LLL:EXT:core/Resources/Private/Language/Form/locallang_tabs.xlf:access,
+            --palette--;;hidden,
+            --palette--;;access,
+    ';
+})();