admin-ui: toasts never mount on the production build (dev server is fine)

[genwave-radio]

🐛 What happens

On the production admin-ui build (the admin_ui image from ./launch.sh), no toast ever appears. The <section aria-label="Notifications alt+T"> mounts empty and [data-sonner-toaster] never appears in the DOM, so toast.success(...) calls are silent.

Seen for "Spot retired." and the new Approve copy on the Ads page. The actions themselves succeed; only the confirmation is missing.

✅ Expected

The same toasts that show on next dev show on the built image.

🔁 Repro

1. BUILD=1 ./launch.sh, sign in, open Ads.
2. Approve or Retire any spot.
3. Inspect: document.querySelector('[data-sonner-toaster]') → null. No toast on screen.
4. Same page on npx next dev → toast renders.

📌 Notes

• Pre-exists gh-Ads: approved spots render one per 10-minute worker tick — approving several in the wizard looks like nothing happened #745: reproduced on main's image 747e5649686b (built 2026-09-10) run as a throwaway container on port 3001.
• <Toaster /> is mounted once in admin-ui/app/(authed)/layout.tsx; sonner 2.0.8 via the @/components/ui/toast wrapper.
• Suspects: the Toaster client boundary tree-shaken or hydrated late in the prod bundle, or sonner's injected styles dropped by the build. Not investigated further.