Fix outer try-catch block structure in checkout route

The outer try block (starting at line 32) was missing its closing catch block.
Added catch block to properly close the outer try statement.

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

src/app/api/checkout/route.ts

@@ -153,4 +153,8 @@ export async function POST(req: Request) {
     console.error('Returning error to client:', message);
     return NextResponse.json({ error: message }, { status: 500 });
   }
+  } catch (err) {
+    const message = err instanceof Error ? err.message : 'Something went wrong.';
+    return NextResponse.json({ error: message }, { status: 500 });
+  }
 }