fix(database): respect Workers PBKDF2 iteration limit

public/db-admin.js

@@ -12,7 +12,9 @@
         'content-type': 'application/json', ...(session ? { 'x-lifeos-admin-session': session } : {}), ...options.headers
       }
     });
-    const result = await response.json();
+    let result;
+    try { result = await response.json(); }
+    catch { throw new Error(text('unexpectedResponse')); }
     if (response.status === 401 && !['login', 'setup', 'password'].includes(path)) { session = null; expiresAt = 0; error = text('sessionExpired'); render(current()); }
     if (!response.ok) throw new Error(result.error || text('requestFailed'));
     return result;