feat(frontend): scaffold Vue 3 + Vite + Tailwind Gruvbox

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/router/index.ts

@@ -0,0 +1,6 @@
+import { createRouter, createWebHistory } from 'vue-router'
+
+export default createRouter({
+  history: createWebHistory(),
+  routes: [],
+})