fix: admin pages not scrollable (content clipped by overflow:hidden)

AdminLayout was a plain div with padding but no scroll. The parent
<main> has overflow:hidden, so admin page content beyond viewport
height was clipped. Added flex:1, overflow:auto, minHeight:0 to
make AdminLayout a proper scroll container.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/Admin/AdminLayout.tsx

@@ -2,7 +2,7 @@ import { Outlet } from 'react-router';
 
 export default function AdminLayout() {
   return (
-    <div style={{ padding: '20px 24px 40px' }}>
+    <div style={{ flex: 1, overflow: 'auto', minHeight: 0, padding: '20px 24px 40px' }}>
       <Outlet />
     </div>
   );