feat(font): Google Fonts preconnect 추가 및 system-ui 폴백 TDD

lib/exporter/html.ts

@@ -254,6 +254,7 @@ function buildHead(page: Page) {
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
     <link rel="canonical" href="/" />
+    <link rel="preconnect" href="https://fonts.googleapis.com" />
     <title>${escapeHtml(page.seo.title)}</title>
     <meta name="description" content="${escapeHtml(page.seo.description)}" />
     <meta property="og:title" content="${escapeHtml(page.seo.title)}" />