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

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

frontend/src/App.vue

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+<template>
+  <RouterView />
+</template>
+<script setup lang="ts">
+import { RouterView } from 'vue-router'
+</script>

frontend/src/main.ts

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+import { createApp } from 'vue'
+import { createPinia } from 'pinia'
+import App from './App.vue'
+import router from './router'
+import './style.css'
+
+createApp(App).use(createPinia()).use(router).mount('#app')

frontend/src/router/index.ts

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

frontend/src/style.css

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+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+body {
+  @apply bg-bg text-text font-mono;
+  min-height: 100vh;
+}
+
+* { box-sizing: border-box; }
+
+::-webkit-scrollbar { width: 6px; }
+::-webkit-scrollbar-track { background: #1d2021; }
+::-webkit-scrollbar-thumb { background: #504945; border-radius: 3px; }