feat: scaffold Vue 3 + TypeScript frontend with lint and typecheck tooling

frontend/src/App.vue

@@ -0,0 +1,8 @@
+<script setup lang="ts"></script>
+
+<template>
+  <main>
+    <h1>discovery-by-llm</h1>
+    <p>Chat interface under construction.</p>
+  </main>
+</template>