Show success stories below the product lists, linked on the category

sys_category gains a story selection and a layout (Options tab, alongside
the images field EXT:news puts there), so one editorial decision serves
every product list that renders the category. ProductListJsonRenderer emits
them beside the products in the 7.3 list envelope; each card carries
forCategories - the product categories it came from - so the front end hides
it with the same ?cat=/?subcat= filter it applies to the products. Stories
are collected over the category and its descendants and deduplicated.

Story links follow the existing rule (detail page's parent path plus slug,
which SuccessStoryPathRewrite maps back), taking the page from the element's
FlexForm or the new site setting vitec.storyDetailPid.

Spec raised to 1.17 with clause 7.15.2.1; the header had been left at 1.12
although entries up to 1.15 already existed, so today's two entries were
renumbered to 1.16 and 1.17.

public/_frontend/index.html

@@ -25,8 +25,8 @@
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
     <title>VITEC</title>
-    <script type="module" crossorigin src="/_frontend/assets/index-CrOmtYLr.js"></script>
-    <link rel="stylesheet" crossorigin href="/_frontend/assets/index-CrFFiPFX.css">
+    <script type="module" crossorigin src="/_frontend/assets/index-BhQWo9uW.js"></script>
+    <link rel="stylesheet" crossorigin href="/_frontend/assets/index-CQJ1iyvA.css">
   </head>
   <body>
     <div id="page"></div>␍