Product list: success stories on the all-products element

The big product list on /products (all products, no category context)
deliberately delivered the empty successStories envelope; the front end
now renders story cards there too and filters them client-side, so the
element aggregates over the WHOLE product category tree instead:

- new allProductCategoryUids(): root category 'Product' (same detection
  as ProductFinderJsonRenderer), children plus descendants depth-first,
  fed through the existing successStoriesFor()
- per-category elements are untouched; forCategories keeps carrying the
  category uids a story is attached to, so the ?cat=/?subcat= filter
  behaves identically on both element kinds
- layout rule unchanged: first contributing category in tree order

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/vitec/Classes/UserFunc/ProductListJsonRenderer.php

@@ -207,9 +207,13 @@ class ProductListJsonRenderer
                 // Success stories the editor attached to these categories
                 // (sys_category, Options tab). They ride along with the list
                 // so the front end can hide them with the same category
-                // filter it applies to the products.
+                // filter it applies to the products. An all-products element
+                // aggregates over the WHOLE product category tree (change
+                // 2026-09-16 on front-end request - it used to deliver the
+                // empty envelope), so forCategories keeps driving the
+                // ?cat=/?subcat= filter exactly like on per-category lists.
                 'successStories' => $this->successStoriesFor(
-                    $allProducts ? [] : $categoryUids,
+                    ($allProducts || $categoryUids === []) ? $this->allProductCategoryUids() : $categoryUids,
                     (int)($settings['storysinglepid'] ?? 0)
                 ),
             ];
@@ -375,6 +379,34 @@ class ProductListJsonRenderer
      * @param int[] $categoryUids
      * @return int[]
      */
+    /**
+     * The whole product category tree - the root's children plus all
+     * descendants in depth-first backend order. Story source for elements
+     * that render all products. Root detection mirrors
+     * ProductFinderJsonRenderer: the root-level sys_category named 'Product'.
+     *
+     * @return int[]
+     */
+    private function allProductCategoryUids(): array
+    {
+        $queryBuilder = GeneralUtility::makeInstance(\TYPO3\CMS\Core\Database\ConnectionPool::class)
+            ->getQueryBuilderForTable('sys_category');
+        $rootUid = (int)($queryBuilder->select('uid')->from('sys_category')
+            ->where(
+                $queryBuilder->expr()->eq('parent', 0),
+                $queryBuilder->expr()->eq('deleted', 0),
+                $queryBuilder->expr()->eq('title', $queryBuilder->createNamedParameter('Product', ParameterType::STRING))
+            )
+            ->setMaxResults(1)
+            ->executeQuery()->fetchOne() ?: 0);
+        if ($rootUid <= 0) {
+            return [];
+        }
+
+        // Drop the root itself - stories hang on the categories below it.
+        return array_values(array_diff($this->expandWithDescendants([$rootUid]), [$rootUid]));
+    }
+
     private function expandWithDescendants(array $categoryUids): array
     {
         $queryBuilder = GeneralUtility::makeInstance(\TYPO3\CMS\Core\Database\ConnectionPool::class)