[Admin] Infra: admin SPA packaging + host serving at /admin #29

[Admin] Infra: admin SPA packaging + host serving at /admin

Why

The current /admin is a single static store/admin/index.html. We want a real React app (matching store/console) served at /admin by the existing host worker — no separate worker or DNS (PAGS is a single self-contained monorepo; see epic architecture decision).

Scope

• Create store/admin/ as a React 19 + TypeScript + Tailwind v4 + Vite app, mirroring the store/console toolchain/build (same design tokens, fonts, dark theme).
• Wire it into the host worker build (workers/host/build.js → pages.ts) so /admin and /admin/* serve the SPA (client-side routing), replacing the static stub.
• Add the admin app to CI build + deploy (.github/workflows), same as console.
• Keep robots: noindex,nofollow.

Acceptance criteria

• /admin serves the new SPA in prod; deep links (/admin/users) resolve to the SPA.
• Old static store/admin/index.html removed.
• Build/deploy runs in CI with no manual steps (push-to-main auto-deploy).
• Shares the design system with console (verified visually).

Relevant code

• workers/host/build.js, workers/host/src/pages.ts
• store/console/ (reference toolchain: vite.config.ts, package.json, Tailwind v4 setup)
• .github/workflows/ (host deploy)

References

• FGS/FAS admin = React SPA served from a CF Worker with Workers Static Assets.

Part of the PAGS Admin Portal epic. Depends on the Foundation issue. Blocks all UI issues.