feat: add OG images, favicon set, manifest and performance tuning

- Build-time Open Graph cards per post and a default card (Satori + Sharp)
- Favicon/ICO/apple-touch/manifest icons generated from one SVG (npm run icons)
- robots.txt and web manifest generated from site.json
- Subset self-hosted fonts to Latin + Turkish (188 KB -> 66 KB) with preload
- Inline the stylesheet to remove the render-blocking request
- Post-build site audit (npm run check:site): h1, alt, SEO tags, links
- Omit canonical on noindex pages

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

astro.config.mjs

@@ -30,6 +30,8 @@ export default defineConfig({
   // Static by default; only routes with `export const prerender = false` (view counter API) run on the server.
   output: 'static',
   adapter: node({ mode: 'standalone' }),
+  // One small stylesheet: inlining it removes a render-blocking request on every page.
+  build: { inlineStylesheets: 'always' },
   integrations: [mdx(), sitemap(), icon({ include: { tabler: ['*'] } }), devRoutes],
   markdown: {
     processor: satteri({ hastPlugins: [figurePlugin, externalLinksPlugin] }),