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>

public/favicon.svg

@@ -1,9 +1 @@
-<svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 128 128">
-    <path d="M50.4 78.5a75.1 75.1 0 0 0-28.5 6.9l24.2-65.7c.7-2 1.9-3.2 3.4-3.2h29c1.5 0 2.7 1.2 3.4 3.2l24.2 65.7s-11.6-7-28.5-7L67 45.5c-.4-1.7-1.6-2.8-2.9-2.8-1.3 0-2.5 1.1-2.9 2.7L50.4 78.5Zm-1.1 28.2Zm-4.2-20.2c-2 6.6-.6 15.8 4.2 20.2a17.5 17.5 0 0 1 .2-.7 5.5 5.5 0 0 1 5.7-4.5c2.8.1 4.3 1.5 4.7 4.7.2 1.1.2 2.3.2 3.5v.4c0 2.7.7 5.2 2.2 7.4a13 13 0 0 0 5.7 4.9v-.3l-.2-.3c-1.8-5.6-.5-9.5 4.4-12.8l1.5-1a73 73 0 0 0 3.2-2.2 16 16 0 0 0 6.8-11.4c.3-2 .1-4-.6-6l-.8.6-1.6 1a37 37 0 0 1-22.4 2.7c-5-.7-9.7-2-13.2-6.2Z" />
-    <style>
-        path { fill: #000; }
-        @media (prefers-color-scheme: dark) {
-            path { fill: #FFF; }
-        }
-    </style>
-</svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><rect width="32" height="32" rx="6" fill="#c95748"/><g transform="translate(4.48 4.48) scale(0.96)"><g fill="none" stroke="#111012" stroke-linecap="round" stroke-linejoin="round" stroke-width="2.4"><path d="M11 12a1 1 0 1 0 2 0a1 1 0 1 0-2 0"/><path d="M16.616 13.924a5 5 0 1 0-9.23 0"/><path d="M20.307 15.469a9 9 0 1 0-16.615 0"/><path d="m9 21l3-9l3 9m-5-2h4"/></g></g></svg>