feat: establish secure update foundation

internal/web/templates/layout.html

@@ -6,8 +6,8 @@
   <meta name="viewport" content="width=device-width, initial-scale=1">
   <meta name="color-scheme" content="light">
   <title>{{.Title}} · DNS Control</title>
-  <link rel="stylesheet" href="/static/styles.css?v=features-21">
-  <script src="/static/app.js?v=features-21" defer></script>
+  <link rel="stylesheet" href="/static/styles.css?v=features-23">
+  <script src="/static/app.js?v=features-23" defer></script>
 </head>
 <body class="page-{{.Page}}">
   <a class="skip-link" href="#main">Zum Inhalt springen</a>
@@ -49,7 +49,7 @@
         <div><span>Neue Version verfügbar</span><strong>{{.SoftwareUpdate.LatestVersion}} ist bereit</strong></div>
         <div class="software-update-banner-actions">
           <a class="button button-quiet" href="/system">Details</a>
-          {{if .SoftwareUpdate.AgentAvailable}}<form action="/system/update" method="post" data-software-update-form><input type="hidden" name="csrf" value="{{.CSRF}}"><input type="hidden" name="version" value="{{.SoftwareUpdate.LatestVersion}}"><button class="button button-primary" type="submit">Jetzt aktualisieren</button></form>{{end}}
+          {{if .SoftwareUpdate.AgentCompatible}}<form action="/system/update" method="post" data-software-update-form><input type="hidden" name="csrf" value="{{.CSRF}}"><input type="hidden" name="version" value="{{.SoftwareUpdate.LatestVersion}}"><button class="button button-primary" type="submit">Jetzt aktualisieren</button></form>{{end}}
         </div>
       </aside>
       {{end}}