feat(ui): adopt Tailwind v4 design system and archive change

- Add tailwindcss v4 + @tailwindcss/vite to mall, shop-admin, admin
- Add @vmall/shared/theme.css tokens with html[data-accent] presets
- Add @vmall/ui kit (VBtn/VBadge/VField/VInput/VCard/VPanel/VTable/VPage,
  VAccentSwatch, useAccent) as a Nuxt module
- Convert all three apps to kit + utilities; delete ui.css/mall.css and
  every <style scoped>; consoles get accent presets, mall locked to red
- Fix VCard boolean prop default (padding) and PDP/store stale
  useAsyncData keys on param navigation
- Archive adopt-tailwind-design-system; new frontend-ui capability spec

openspec/config.yaml

@@ -6,7 +6,7 @@ context: |
   Tech stack:
   - Backend: Rust (axum 0.8, sqlx 0.8 + Postgres 18, redis 8, JWT, argon2) at apps/api, crate vmall-api. Modular monolith: handler → service → repository under src/modules/<context> (docs/adr/0001, docs/tech-specs/rust-api.md). HTTP REST is the public contract; GraphQL is not the primary API (docs/adr/0002). Money is stored as integer minor units + ISO currency code; never floats.
   - Frontends: three Nuxt 3 apps in pnpm workspace: apps/mall (customer storefront, port 3000), apps/shop-admin (merchant console, 3001), apps/admin (platform console, 3002).
-  - Shared contract: packages/shared (@vmall/shared) — TS types, API client, en/zh locales, ui.css. Frontends must use it; no per-app API reimplementation.
+  - Shared contract: packages/shared (@vmall/shared) — TS types, API client, en/zh locales, Tailwind v4 theme.css. Frontends must use it; no per-app API reimplementation. Shared Vue primitives live in packages/ui (@vmall/ui, Nuxt module); layout uses Tailwind utilities, no <style scoped>.
   - Dev infra: Postgres + Redis run in local docker (containers pg18, rdb8); databases vmall / vmall_test; API runs migrations on boot (sqlx migrate).
 
   Conventions: