ci(website): Cloudflare Pages deploy via Gitea Actions

New .gitea/workflows/website.yaml: on a push to main or website that
touches website/**, build the Astro site with pnpm and deploy
website/dist to the `relplay` Cloudflare Pages project via wrangler —
--branch selects production (main) vs preview (website). Runs on the
bare ci-public runner (node present; pnpm via corepack). Pin pnpm with
package.json's packageManager for deterministic corepack installs.

Requires repo Actions secrets CLOUDFLARE_API_TOKEN + CLOUDFLARE_ACCOUNT_ID.

website/package.json

@@ -3,6 +3,7 @@
   "private": true,
   "type": "module",
   "version": "0.0.1",
+  "packageManager": "pnpm@10.30.3",
   "scripts": {
     "dev": "astro dev",
     "start": "astro dev",