feat(site): 🚀 add Astro marketing/content site

Standalone Astro 6 site in /site (decoupled from the /web app monorepo):
landing page, /blog with one post (Content Layer), and terms/privacy/cookie
legal pages. Pure Astro, server-rendered to static HTML.

- Static by default via @astrojs/vercel adapter; any route can opt into SSR
  with `export const prerender = false` (deploys as a Vercel Function).
- SPA-style navigation with <ClientRouter />, transition:persist on the header
  (no icon flash), and viewport prefetch — ~6 KB gzip JS, no React.
- Deploy on Vercel by setting Root Directory to 'site' (no vercel.json needed).

See site/README.md for dev and deploy instructions.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

site/README.md

@@ -0,0 +1,75 @@
+# site
+
+Public-facing marketing/content site for the KiCad WebAssembly project: landing
+page, blog, and legal pages. Built with **Astro 6**.
+
+This is a **standalone** project — it is intentionally decoupled from the `/web`
+app monorepo (which is the product itself: React frontend + Fastify backend).
+It uses **npm** (not the monorepo's pnpm) and has its own `package-lock.json`.
+
+## What it ships
+
+- Static by default: every page is prerendered to HTML and ships **zero client
+  JavaScript**. A visitor downloads HTML + CSS only — no React/JS bundle.
+- SSR-capable: the Vercel adapter is wired in, so any individual route can be
+  switched to per-request server rendering without ripping anything out (see
+  below).
+
+## Routes
+
+| Route                 | Source                                  |
+| --------------------- | --------------------------------------- |
+| `/`                   | `src/pages/index.astro`                 |
+| `/blog`               | `src/pages/blog/index.astro`            |
+| `/blog/<id>`          | `src/pages/blog/[slug].astro`           |
+| `/terms`              | `src/pages/terms.astro`                 |
+| `/privacy`            | `src/pages/privacy.astro`               |
+| `/cookies`            | `src/pages/cookies.astro`               |
+
+Blog posts are Markdown files in `src/content/blog/`, validated by the schema in
+`src/content.config.ts`. Add a post by dropping a new `.md` file there with
+`title`, `description`, and `pubDate` frontmatter.
+
+## Local development
+
+Requires **Node ≥ 22.12** (Astro 6 requirement).
+
+```bash
+cd site
+npm install
+npm run dev        # http://localhost:4321
+npm run build      # outputs to dist/ (+ .vercel/output for the adapter)
+npm run preview    # serve the production build locally
+```
+
+## SSR per route
+
+Pages are static by default. To render a specific page or endpoint on demand
+(per request, as a Vercel Function), add this to its frontmatter:
+
+```astro
+---
+export const prerender = false;
+---
+```
+
+That's the only change needed — the `@astrojs/vercel` adapter in
+`astro.config.mjs` already provides the server runtime. The rest of the site
+stays static.
+
+## Deploying to Vercel
+
+The `@astrojs/vercel` adapter emits the Vercel Build Output API format, so **no
+`vercel.json` is required**.
+
+1. Push this repo to GitHub.
+2. Vercel dashboard → **New Project** → import this repo.
+3. Click **Edit** next to **Root Directory** and set it to **`site`**. This is
+   the standard way to deploy a project that lives in a subdirectory.
+4. Vercel auto-detects the **Astro** framework preset and the package manager
+   from the lockfile. Leave the build/install commands at their defaults.
+5. Deploy. Static pages are served from the CDN; any route with
+   `prerender = false` is deployed as a Vercel Function automatically.
+
+Note: do **not** use `vercel.json` for URL rewrites with Astro — use Astro's
+`redirects` option in `astro.config.mjs` instead.