fix(frontend): harden CTE step semantics and padding

frontend/src/viewers/CtePlanViewer.tsx

@@ -67,7 +67,7 @@ function CteCard({ cte, total }: { cte: CtePlanCte; total: number }) {
 
   return (
     <Card className="gap-0 rounded-lg border py-0 shadow-none">
-      <CardHeader className="gap-3 rounded-t-lg border-b border-border/60 bg-muted/15 p-4 sm:p-5">
+      <CardHeader className="gap-3 rounded-t-lg border-b border-border/60 bg-muted/15 p-4 sm:p-5 sm:[&.border-b]:pb-5">
         <div className="grid min-w-0 grid-cols-[auto_minmax(0,1fr)] items-center gap-2.5">
           <Badge variant="outline" className="font-mono">
             CTE {cte.index}/{total}
@@ -203,11 +203,13 @@ export function CtePlanViewer({ plan }: { plan: CtePlanV2 }) {
         </div>
       </div>
 
-      <div className="flex flex-col gap-3">
+      <ol aria-label="CTE plan steps" className="flex flex-col gap-3">
         {plan.ctes.map((cte) => (
-          <CteCard key={cte.name} cte={cte} total={plan.ctes.length} />
+          <li key={cte.name} className="min-w-0">
+            <CteCard cte={cte} total={plan.ctes.length} />
+          </li>
         ))}
-      </div>
+      </ol>
     </div>
   );
 }