feat(ui): add admin area (domains, profiles, backup) with gear link in header

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/routes/+layout.svelte

@@ -12,7 +12,10 @@
 
 <header class="bar">
   <a href="/" class="brand">Kochwas</a>
-  <ProfileSwitcher />
+  <div class="bar-right">
+    <a href="/admin" class="admin-link" aria-label="Einstellungen">⚙️</a>
+    <ProfileSwitcher />
+  </div>
 </header>
 
 <main>
@@ -51,6 +54,24 @@
     text-decoration: none;
     color: #2b6a3d;
   }
+  .bar-right {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+  }
+  .admin-link {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 40px;
+    height: 40px;
+    border-radius: 999px;
+    text-decoration: none;
+    font-size: 1.15rem;
+  }
+  .admin-link:hover {
+    background: #f4f8f5;
+  }
   main {
     padding: 0 1rem 4rem;
     max-width: 760px;