Products megamenu as a data-driven catalog with a Solr product type-ahead

- evo_megamenu_json stays project-neutral: new panel layout "catalog";
  for such entries the MenuBuilder dispatches the new PSR-14 event
  BuildCatalogEvent and emits whatever a listener sets as `catalog`
  (null without a listener). The entry's teaser cards serve as the
  featured tiles; the teaser inline field now also shows for "catalog",
  and the entry form reloads when the layout changes. README section
  "Layout catalog"
- VITEC listener ProvideProductCatalog fills it, modelled on the Ross
  Video products menu: main categories below the "Product" root, their
  subcategories as groups, products with a plain-text one-line teaser;
  same visibility rules as the product list, Product Finder links
  (/products?cat=&subcat=), empty categories and groups left out, three
  queries for the whole catalog
- Product type-ahead GET /_json/?type=7385&q= (USER_INT page type,
  ProductMenuSearchJsonRenderer): Solr restricted to products, last term
  completed as a prefix, up to six product cards plus their titles as
  autocomplete suggestions; endpoint announced in catalog.search
- Spec v1.23 (clause 7.16: product type-ahead)

packages/evo_megamenu_json/README.md

@@ -17,9 +17,10 @@ A plugin called **Megamenu**. Inside it:
 | **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).
+Three panel layouts per entry: `columns` for a structure menu (products,
+solutions, markets), `teasers` for a small link column next to cards
+(news, stories), and `catalog` for a data-driven panel whose content comes
+from the site package (see below).
 
 ## Installation
 
@@ -89,6 +90,31 @@ An item whose target page does not exist yet carries `"pending": true`.
 column heading instead), `mute` (show, not clickable) or `hide`. This keeps
 a menu shippable while its deeper pages are still being built.
 
+### Layout `catalog`
+
+For panels built from data rather than by hand — a product catalog with
+categories, groups and items, a search bar, whatever the site needs. The
+extension stays project-neutral: it dispatches
+`Evomedien\EvoMegamenuJson\Event\BuildCatalogEvent` for every catalog entry
+and emits whatever a listener sets via `setCatalog()` verbatim as
+`catalog` on the entry (`null` without a listener). The entry's teaser cards
+are emitted as `teasers` as usual and serve as the panel's featured tiles;
+its columns are ignored.
+
+```php
+#[AsEventListener(identifier: 'site/megamenu-catalog')]
+final class ProvideCatalog
+{
+    public function __invoke(BuildCatalogEvent $event): void
+    {
+        $event->setCatalog(['categories' => [/* … */]]);
+    }
+}
+```
+
+`getEntry()` hands the listener the raw entry row (to tell several catalog
+entries apart), `getStage()` the content stage.
+
 ## Notes
 
 * Every link is a resolved URL — page, record, external or file, run through