Design pass: visual alignment with the Ghost blog

Fixed-dark theme matching blog.c0smere.net (Source theme + injections):
bg #0b0d12, white/64%-white text, accent green #218107 (links lifted to
#2fa50f for contrast). Self-hosted JetBrains Mono + Libre Baskerville —
the same woff2 files the blog serves. Site header with logo + nav
mirroring gh-head; serif-italic quotes; blog-style borderless tables;
single dark shiki/mermaid theme; homepage styled as a typographic feed.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

astro.config.mjs

@@ -13,8 +13,7 @@ export default defineConfig({
   markdown: {
     remarkPlugins: [[remarkObsidian, { slugMap }], remarkMath],
     rehypePlugins: [rehypeKatex],
-    shikiConfig: {
-      themes: { light: 'github-light', dark: 'github-dark' },
-    },
+    // single dark theme — the site is fixed-dark to match blog.c0smere.net
+    shikiConfig: { theme: 'github-dark' },
   },
 });