Show app version in admin UI and /version endpoint

Embed APP_VERSION build arg in Docker image (default: dev).
build_push.sh passes the git tag as build arg. Proxy exposes
GET /version, admin UI shows it as read-only field in settings.

frontend/src/main.jsx

@@ -82,6 +82,7 @@ function SettingsSection({ password }) {
   const [modelsLoading, setModelsLoading] = useState(false);
   const [ollamaReachable, setOllamaReachable] = useState(true);
   const [proxyEndpoint, setProxyEndpoint] = useState(null);
+  const [appVersion, setAppVersion] = useState(null);
   const [saved, setSaved] = useState(false);
   const [error, setError] = useState(null);
 
@@ -115,6 +116,7 @@ function SettingsSection({ password }) {
       const s = settingsRes.data;
       setSettings(s);
       setProxyEndpoint(proxyRes.data.endpoint);
+      setAppVersion(proxyRes.data.version);
       fetchModels(s.ollama_url, s.force_model);
     }).catch(() => setError('Einstellungen konnten nicht geladen werden.'));
   }, []);
@@ -145,6 +147,10 @@ function SettingsSection({ password }) {
             <small> (Änderung erfordert Neustart)</small>
           </span>
         </div>
+        <div className="settings-row">
+          <label>Version</label>
+          <span className="settings-value">{appVersion ?? '…'}</span>
+        </div>
         <div className="settings-row">
           <label>Ollama-Endpunkt</label>
           <div className="settings-input-wrap">