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

migrations/check_megamenu_schema.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * Read-only: is the evo_megamenu_json schema in place?
+ * Checks the four menu tables and the inline column on tt_content.
+ *
+ * Usage:  php migrations/check_megamenu_schema.php
+ */
+
+$root = null;
+$dir = __DIR__;
+for ($i = 0; $i < 5; $i++) {
+    if (is_file($dir . '/config/system/settings.php')) { $root = $dir; break; }
+    $dir = dirname($dir);
+}
+if ($root === null) { exit("Could not locate project root above " . __DIR__ . "\n"); }
+
+$settings = require $root . '/config/system/settings.php';
+$db = $settings['DB']['Connections']['Default'];
+$pdo = new PDO(
+    sprintf('mysql:host=%s;port=%s;dbname=%s;charset=utf8mb4', $db['host'] ?? 'localhost', $db['port'] ?? 3306, $db['dbname'] ?? ''),
+    $db['user'] ?? '', $db['password'] ?? '',
+    [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC]
+);
+
+$tables = [
+    'tx_evomegamenujson_entry',
+    'tx_evomegamenujson_column',
+    'tx_evomegamenujson_item',
+    'tx_evomegamenujson_teaser',
+];
+$missing = 0;
+foreach ($tables as $table) {
+    $exists = (bool)$pdo->query("SHOW TABLES LIKE " . $pdo->quote($table))->fetchColumn();
+    $count = $exists ? (int)$pdo->query("SELECT COUNT(*) FROM `$table`")->fetchColumn() : 0;
+    printf("%-32s %s%s\n", $table, $exists ? 'OK' : 'FEHLT', $exists ? "  ($count Datensaetze)" : '');
+    $missing += $exists ? 0 : 1;
+}
+
+$col = $pdo->query("SHOW COLUMNS FROM tt_content LIKE 'tx_evomegamenujson_entries'")->fetch();
+printf("%-32s %s\n", 'tt_content.tx_..._entries', $col ? 'OK' : 'FEHLT');
+$missing += $col ? 0 : 1;
+
+$ce = (int)$pdo->query("SELECT COUNT(*) FROM tt_content WHERE deleted = 0 AND CType = 'evomegamenujson_megamenu'")->fetchColumn();
+printf("%-32s %d\n", 'Megamenu-Elemente angelegt', $ce);
+
+echo "\n" . ($missing === 0
+    ? "Schema vollstaendig - Plugin kann angelegt werden.\n"
+    : "$missing Objekt(e) fehlen - Schema-Update noetig.\n");