feat(website): add OG hero preview image for link sharing

Replace the raw logo OG image with a designed 1200×630 hero card
generated at build time using satori + @resvg/resvg-js.

- Add generate-og.ts script with branded dark card design (gradient
  orbs, geometric rings, logo, title, tagline)
- Wire generation into build pipeline (runs before astro build)
- Update meta tags with absolute URLs, dimensions, and twitter:image
- Configure site URL (https://aryx.app) in astro.config.mjs

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/astro.config.mjs

@@ -2,6 +2,7 @@ import { defineConfig } from 'astro/config';
 import tailwindcss from '@tailwindcss/vite';
 
 export default defineConfig({
+  site: 'https://aryx.app',
   vite: {
     plugins: [tailwindcss()],
   },