Add ja roadmap page (falls back to en content)

src/pages/ja/roadmap.astro

@@ -0,0 +1,15 @@
+---
+  import '../../styles/main.css'
+  import XahauRoadmap from '../../components/XahauRoadmap.astro'
+  import BaseLayout from '../../layouts/BaseLayout.astro'
+
+  const _frontmatter = {
+    title: 'ロードマップ',
+    description: 'Xahau roadmap across the upcoming quarters',
+  }
+---
+<BaseLayout frontmatter={_frontmatter}>
+  <div class="page-content flex-1 container mx-auto max-w-7xl p-6">
+    <XahauRoadmap lang="ja" theme="light"/>
+  </div>
+</BaseLayout>