Add a KantTresor tab to the central registry

KantTresor instances (from 1.82.0) report to /api/kanttresor/melden with the
same key-then-HMAC protocol. The new tab lists them with tenants, disk usage
and failing services; it never offers or accepts an update order, since
KantTresor is updated with ./update.sh on the server. See ADR 124.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

zentrale/app/vorlagen/rahmen.php

@@ -6,8 +6,8 @@
 <meta name="viewport" content="width=device-width, initial-scale=1">
 <meta name="robots" content="noindex, nofollow">
 <title><?= $v->e($titel) ?> · KantSites Zentrale</title>
-<link rel="stylesheet" href="/app.css?v=3">
-<script src="/app.js?v=1" defer></script>
+<link rel="stylesheet" href="/app.css?v=4">
+<script src="/app.js?v=2" defer></script>
 <link rel="icon" href="data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 32 32'%3E%3Crect width='32' height='32' rx='7' fill='%23173f6b'/%3E%3Cpath d='M9 8v16M9 16l9-8M12.5 13l7 11' stroke='%23fff' stroke-width='3.2' fill='none' stroke-linecap='round'/%3E%3C/svg%3E">
 </head>
 <body>
@@ -24,6 +24,15 @@
     <?php } ?>
   </div>
 </header>
+<?php if (null !== $konto) { ?>
+  <nav class="reiter" aria-label="Produkte">
+    <ul class="reiter-innen">
+      <?php foreach (['kantsites' => ['/', 'KantSites'], 'kanttresor' => ['/kanttresor', 'KantTresor']] as $name => [$ziel, $text]) { ?>
+        <li><a href="<?= $ziel ?>"<?= $produkt === $name ? ' aria-current="page"' : '' ?>><?= $text ?></a></li>
+      <?php } ?>
+    </ul>
+  </nav>
+<?php } ?>
 <main id="inhalt" class="seite" tabindex="-1">
   <?php if (null !== $hinweis) { ?>
     <p class="hinweis hinweis-<?= $v->e($hinweis['art']) ?>" role="<?= 'fehler' === $hinweis['art'] ? 'alert' : 'status' ?>"><?= $v->e($hinweis['text']) ?></p>