feat: migrate to Astro's experimental font API

Replace @fontsource-variable NPM packages with Astro's built-in
experimental font API using the Fontsource provider. Fonts are now
fetched at build time, cached locally, and served with the site.

This provides automatic @font-face generation, preload link injection,
and metric-adjusted fallback fonts (size-adjust, ascent-override, etc.)
to reduce CLS during font loading.

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

astro.config.mjs

@@ -1,4 +1,4 @@
-import { defineConfig } from "astro/config";
+import { defineConfig, fontProviders } from "astro/config";
 import tailwindcss from "@tailwindcss/vite";
 import sitemap from "@astrojs/sitemap";
 import icon from "astro-icon";
@@ -10,4 +10,29 @@ export default defineConfig({
   vite: {
     plugins: [tailwindcss()],
   },
+  experimental: {
+    fonts: [
+      {
+        provider: fontProviders.fontsource(),
+        name: "Bricolage Grotesque",
+        cssVariable: "--font-bricolage",
+        weights: ["200 800"],
+        fallbacks: ["system-ui", "sans-serif"],
+      },
+      {
+        provider: fontProviders.fontsource(),
+        name: "DM Sans",
+        cssVariable: "--font-dm-sans",
+        weights: ["100 1000"],
+        fallbacks: ["system-ui", "sans-serif"],
+      },
+      {
+        provider: fontProviders.fontsource(),
+        name: "JetBrains Mono",
+        cssVariable: "--font-jetbrains",
+        weights: ["100 800"],
+        fallbacks: ["SF Mono", "Consolas", "monospace"],
+      },
+    ],
+  },
 });