fe_comment: Feedback Overview content element in the page JSON

- New content element "Feedback Overview" (CType fecomment_overview):
  the current FE user's feedback state under content.feedbackOverview,
  so the overview page renders like any other page instead of a
  front-end special case
- Rendered as USER_INT inside the cached page JSON (EXT:headless replaces
  the field per request): data is per user, visitors without a session
  get {"allowed": false} - verified that nothing leaks from the cache
- One implementation for both consumers: the new FeedbackState service
  builds the state payload; the API middleware delegates to it
- State payload (API and element) gained canSubmit and actions (all
  write endpoints with method and URL), so the front end needs no
  hard-coded endpoints for the submit button below the ticket list
- New site set evomedien/fe-comment carries the TypoScript, added to the
  site configuration; icon fecomment-overview

public/_frontend/index.html

@@ -23,8 +23,8 @@
     <meta name="twitter:description" content="Enterprise IPTV, video streaming, and digital signage solutions." />
     <link rel="icon" type="image/svg+xml" href="/fileadmin/icons/favicon.ico" />
     <title>VITEC</title>
-    <script type="module" crossorigin src="/_frontend/assets/index-Dvbm25nF.js"></script>
-    <link rel="stylesheet" crossorigin href="/_frontend/assets/index-PE6EdhLv.css">
+    <script type="module" crossorigin src="/_frontend/assets/index-B1plOsdz.js"></script>
+    <link rel="stylesheet" crossorigin href="/_frontend/assets/index-BADFa6PF.css">
   </head>
   <body>
     <div id="page"></div>␍