## Why

The Astro project scaffold exists but has no Tailwind CSS integration or brand tokens configured. Before any UI work can begin, the design system foundation must be in place: brand colors, the Archia typeface, and the gradient — all wired into Tailwind so every subsequent step can use utility classes directly.

## What Changes

- Install `tailwindcss` and `@tailwindcss/vite` (Tailwind v4) and `@astrojs/sitemap`
- Configure `astro.config.mjs` with the Vite Tailwind plugin and sitemap integration
- Create `src/styles/global.css` with:
  - `@import "tailwindcss"`
  - `@theme` block defining brand color tokens and `font-archia`
  - `@font-face` declarations for all 6 Archia weights (Thin, Light, Regular, Medium, SemiBold, Bold)
- Replace the default `src/pages/index.astro` with a brand smoke test page showing color swatches, font weight samples, and a gradient bar
- No `tailwind.config.mjs` — configuration is CSS-based (Tailwind v4 pattern)

## Capabilities

### New Capabilities

- `brand-tokens`: Qumo design system tokens available as Tailwind utilities — brand colors (`midnight`, `snow`, `brand-blue`, `brand-red`), `font-archia`, and the gradient definition

### Modified Capabilities

_(none)_

## Impact

- `website/package.json` — new dependencies: `tailwindcss`, `@tailwindcss/vite`, `@astrojs/sitemap`
- `website/astro.config.mjs` — adds Vite plugin and sitemap integration
- `website/src/styles/global.css` — new file, imported globally
- `website/src/pages/index.astro` — replaced with temporary smoke test (will be replaced again in a later step when the homepage is built)
- No SEO impact — smoke test page is a dev-only visual check
- No content strings needed — smoke test has no user-visible text to localize
