Add urapt-web: web UI for urapt-server instances

A Vite + React 18 + TypeScript SPA, same-origin with the API (no CORS,
no Go server changes). Full management parity with the urapt CLI:

- First-run setup (admin bootstrap via needs_setup), login/logout
- Repositories: list, create, tabbed detail (overview edit/delete,
  members CRUD, distributions/components/architectures manager,
  package list + .deb upload + detail + delete, apt-config panel)
- API tokens: show-once creation + revoke
- Admin users: toggle admin / delete
- Settings + dark mode

Stack: Tailwind + shadcn/ui (New York), React Router v7 (lazy routes),
TanStack Query v5, Zustand, Vitest. Hand-written typed API client
mirroring shared/api + shared/models. Dev proxy forwards /api + /apt
to a local urapt-server; deploy behind nginx/Caddy (see urapt-web/README).

urapt-web/.nvmrc

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+20