fe_comment: recipients are the FE users of the feedback group

- The selectable recipients are no longer a hand-maintained setting but
  every active frontend user of the feedback group (feUserGroup) with a
  valid e-mail address; the id is the fe_users uid, so a stored selection
  survives users joining or leaving. The `recipients` setting is marked
  unused
- Each recipient in the state payload carries label, email and selected
  (the stored choice), for a checkbox list with "select all" above the
  submit button
- submit accepts the checked ids directly ({"recipients": [uids]}),
  validates them against the group, stores and uses them, and reports
  the addresses used as sentTo; no selection falls back to mailTo
- migrations/check_fecomment_user.php: all summaries and items of one
  user incl. deleted ones, for diagnosis

migrations/check_fecomment_user.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Diagnose: all fe_comment summaries and items of one FE user, including
+ * deleted ones, with timestamps. Notes are shortened, no secrets printed.
+ *   php migrations/check_fecomment_user.php 2
+ */
+$feUser = (int)($argv[1] ?? 0);
+if ($feUser <= 0) {
+    fwrite(STDERR, "Aufruf: php migrations/check_fecomment_user.php <fe_users-uid>\n");
+    exit(1);
+}
+$settings = require __DIR__ . '/../config/system/settings.php';
+$db = $settings['DB']['Connections']['Default'];
+$pdo = new PDO('mysql:host=' . $db['host'] . ';dbname=' . $db['dbname'] . ';charset=utf8mb4', $db['user'], $db['password']);
+$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+
+$summaries = $pdo->prepare(
+    "SELECT uid, status, deleted, FROM_UNIXTIME(crdate) AS created, FROM_UNIXTIME(tstamp) AS changed,
+            FROM_UNIXTIME(NULLIF(sent_at,0)) AS sent, recipients, CHAR_LENGTH(general_notes) AS notes_len
+       FROM tx_fecomment_summary WHERE fe_user = ? ORDER BY uid"
+);
+$summaries->execute([$feUser]);
+$items = $pdo->prepare(
+    "SELECT uid, deleted, FROM_UNIXTIME(crdate) AS created, FROM_UNIXTIME(tstamp) AS changed, url,
+            CHAR_LENGTH(note) AS note_len
+       FROM tx_fecomment_feedback WHERE summary = ? ORDER BY sorting"
+);
+foreach ($summaries->fetchAll(PDO::FETCH_ASSOC) as $s) {
+    echo "Summary {$s['uid']} | status={$s['status']} deleted={$s['deleted']} | erstellt {$s['created']} | geaendert {$s['changed']}"
+        . ($s['sent'] ? " | gesendet {$s['sent']}" : '') . " | recipients=[{$s['recipients']}] | general_notes " . (int)$s['notes_len'] . " Zeichen\n";
+    $items->execute([(int)$s['uid']]);
+    foreach ($items->fetchAll(PDO::FETCH_ASSOC) as $i) {
+        echo "    Item {$i['uid']} | deleted={$i['deleted']} | erstellt {$i['created']} | geaendert {$i['changed']} | note " . (int)$i['note_len'] . " Zeichen | {$i['url']}\n";
+    }
+}