Update theme to Astro v6 stable and switch to built-in Fonts API

* Updated theme to Astro v6 stable
* Replaced third-party astro-font with the built-in Fonts API

astro.config.mjs

@@ -3,11 +3,46 @@ import react from "@astrojs/react";
 import sitemap from "@astrojs/sitemap";
 import tailwindcss from "@tailwindcss/vite";
 import AutoImport from "astro-auto-import";
-import { defineConfig } from "astro/config";
+import { defineConfig, fontProviders } from "astro/config";
 import remarkCollapse from "remark-collapse";
 import remarkToc from "remark-toc";
 import sharp from "sharp";
 import config from "./src/config/config.json";
+import theme from "./src/config/theme.json";
+
+// Helper to parse font string format: "FontName:wght@400;500;600;700"
+function parseFontString(fontStr) {
+  const [name, weightPart] = fontStr.split(":");
+  let weights = [400]; // default weight
+
+  if (weightPart) {
+    // Extract weights from wght@400;500;600 format
+    const weightMatch = weightPart.match(/wght@?([\d;]+)/);
+    if (weightMatch) {
+      weights = weightMatch[1].split(";").map((w) => parseInt(w, 10));
+    }
+  }
+
+  return { name, weights };
+}
+
+// Build fonts configuration from theme.json
+const fontsConfig = Object.entries(theme.fonts.font_family)
+  .filter(([key]) => !key.includes("_type")) // Filter out type entries
+  .map(([key, fontStr]) => {
+    const { name, weights } = parseFontString(fontStr);
+    const typeKey = `${key}_type`;
+    const fallback = theme.fonts.font_family[typeKey] || "sans-serif";
+
+    return {
+      name,
+      cssVariable: `--font-${key}`,
+      provider: fontProviders.google(),
+      weights,
+      display: "swap",
+      fallbacks: [fallback],
+    };
+  });
 
 // https://astro.build/config
 export default defineConfig({
@@ -16,6 +51,7 @@ export default defineConfig({
   trailingSlash: config.site.trailing_slash ? "always" : "never",
   image: { service: sharp() },
   vite: { plugins: [tailwindcss()] },
+  fonts: fontsConfig,
   integrations: [
     react(),
     sitemap(),