feat(ui): show spinner on the Stop confirm button while the stop call is in flight

The AlertDialog from the design system already exposes a `loading` prop that
swaps the confirm button into a spinner state. Wire it to
stopDeployment.isPending so users get feedback during the (sometimes multi-
second) container-stop call instead of staring at a static button.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/AppsTab/AppDeploymentPage/index.tsx

@@ -604,6 +604,7 @@ export default function AppDeploymentPage() {
         description="This will stop the running container. The app will be unavailable until redeployed."
         confirmLabel="Stop"
         variant="danger"
+        loading={stopDeployment.isPending}
       />
 
       {/* ── Delete confirmation dialog ── */}