fix: constrain admin layout to container width matching rest of site

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/routes/admin/+layout.svelte

@@ -14,7 +14,9 @@
   }
 </script>
 
-<div class="flex min-h-screen bg-background">
+<div class="min-h-screen bg-background">
+  <div class="container mx-auto px-4">
+    <div class="flex min-h-screen">
       <!-- Sidebar -->
       <aside class="w-56 shrink-0 border-r border-border/40 bg-card/60 backdrop-blur-sm flex flex-col">
         <div class="px-4 py-5 border-b border-border/40">
@@ -45,4 +47,6 @@
       <main class="flex-1 overflow-auto">
         {@render children()}
       </main>
+    </div>
+  </div>
 </div>