Switch to Playwrite US Modern + Imprima fonts

- Headings: Playwrite US Modern (extralight/200 weight)
- Body: Imprima (400 weight)
- Keep Geist Mono for code blocks

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

package.json

@@ -16,6 +16,8 @@
     "@astrojs/sitemap": "^3.6.0",
     "@fontsource/geist-mono": "^5.2.7",
     "@fontsource/geist-sans": "^5.2.5",
+    "@fontsource/imprima": "^5.2.8",
+    "@fontsource/playwrite-us-modern": "^5.2.7",
     "@tailwindcss/vite": "^4.1.13",
     "astro": "^5.13.9",
     "astro-pagefind": "^1.8.5",