Fix loading state not being cleared when design data loads successfully

The setLoading(false) call was only in the catch block, so when the API
call succeeded, the page would stay in a "Loading..." state indefinitely.
Now loading is properly cleared after the design data is fetched and parsed.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/admin/designs/[id]/edit/page.tsx

@@ -61,6 +61,7 @@ export default function EditDesignPage({ params }: { params: { id: string } }) {
           }
         }
         setDesign(data);
+        setLoading(false);
       })
       .catch((err) => {
         console.error('Error fetching design:', err);