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/README.md

@@ -0,0 +1,101 @@
+# EVO Megamenu JSON
+
+An editable megamenu for headless TYPO3. One content element holds the whole
+menu; the extension publishes it as JSON, the front end renders it.
+
+Project-neutral by design — nothing in here knows which site it runs on.
+
+## What the editor gets
+
+A plugin called **Megamenu**. Inside it:
+
+| Level | Holds |
+|---|---|
+| **Entry** | one item in the main bar: label, target page, panel layout |
+| **Column** | a heading (optionally a link) and its items |
+| **Item** | label, link, teaser line, badge, thumbnail, “page not ready” flag |
+| **Teaser card** | kicker, headline, text, link, image — for editorial panels |
+| **Featured** | one highlighted block per entry, edited on the entry itself |
+
+Two panel layouts per entry: `columns` for a structure menu (products,
+solutions, markets) and `teasers` for a small link column next to cards
+(news, stories).
+
+## Installation
+
+```bash
+composer require evomedien/evo-megamenu-json
+vendor/bin/typo3 extension:setup
+vendor/bin/typo3 database:updateschema "*.add,*.change"
+```
+
+In the site configuration, add the set **EVO Megamenu (JSON)** and set:
+
+| Setting | Meaning |
+|---|---|
+
+| `megamenu.contentUid` | uid of the Megamenu element to publish on every page |
+| `megamenu.storagePid` | alternative: folder whose first Megamenu element is used |
+
+Leave both uid and pid at 0 and the menu is only rendered where the element
+sits — useful while building it.
+
+## Payload
+
+```json
+"megaMenu": {
+  "settings": {
+    "stage": 3, "openOn": "hover", "closeDelay": 140, "columnsPerRow": 4,
+    "panelWidth": "container", "pendingBehaviour": "fallback",
+    "showCounts": true, "showViewAll": true, "viewAllLabel": "View all %s"
+  },
+  "entries": [
+    {
+      "title": "Products",
+      "link": "/products",
+      "layout": "columns",
+      "columns": [
+        {
+          "title": "IP Video Streaming",
+          "link": "/products/ip-video-streaming",
+          "items": [
+            { "title": "Appliances", "link": "/products/ip-video-streaming/appliances",
+              "pending": true, "teaser": "MGW Diamond, Ace, Pico",
+              "image": { "url": "/fileadmin/...", "alternative": "", "title": "", "width": 600, "height": 400 } }
+          ]
+        }
+      ],
+      "featured": { "kicker": "Datasheet", "title": "MGW Diamond-H", "text": "…", "link": "/product/…", "image": { } }
+    }
+  ]
+}
+```
+
+`settings` travels with the menu on purpose: the front end reads hover
+behaviour, close delay, column count and labels from the payload instead of
+hard-coding them, so an editor can change them without a deploy.
+
+### Content stages
+
+`stage` decides how much detail is emitted — 1 structure only, 2 adds images,
+teaser lines and cards, 3 adds the featured block. Later stages only **add**
+keys, so a front end written for stage 1 keeps working when the stage is
+raised.
+
+### `pending`
+
+An item whose target page does not exist yet carries `"pending": true`.
+`settings.pendingBehaviour` says what to do with it: `fallback` (link to the
+column heading instead), `mute` (show, not clickable) or `hide`. This keeps
+a menu shippable while its deeper pages are still being built.
+
+## Notes
+
+* Every link is a resolved URL — page, record, external or file, run through
+  typolink at render time.
+* Translations are overlaid per record, so a menu can be localised entry by
+  entry.
+* The renderer never throws: a broken menu returns an empty value rather than
+  taking the page payload down.
+* Without `friendsoftypo3/headless` the element has no JSON envelope to render
+  into — the extension is built for headless installations.