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

packages/fe_comment/Configuration/TCA/Overrides/tt_content.php

@@ -0,0 +1,25 @@
+<?php
+
+defined('TYPO3') or die();
+
+// "Feedback Overview": the current FE user's feedback state as JSON
+// (content.feedbackOverview, rendered by OverviewJsonRenderer). Place it on
+// the overview page (extension setting overviewPid). No plugin options.
+\TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addPlugin(
+    [
+        'label' => 'Feedback Overview',
+        'description' => 'The logged-in user\'s open feedback summary (items, attachments, notes, recipients) as JSON for the front end.',
+        'value' => 'fecomment_overview',
+        'icon' => 'fecomment-overview',
+        'group' => 'plugins',
+    ],
+    'CType',
+    'fe_comment'
+);
+
+$GLOBALS['TCA']['tt_content']['types']['fecomment_overview']['showitem'] = '
+    --div--;LLL:EXT:core/Resources/Private/Language/Form/locallang_tabs.xlf:general,
+        --palette--;;general,
+        --palette--;;headers,
+    --div--;LLL:EXT:core/Resources/Private/Language/Form/locallang_tabs.xlf:access,
+        --palette--;;hidden';