T-1: initialize monorepo structure with backend and frontend scaffolds

Backend: Spring Boot 3.5.11 on Java 25, Maven with wrapper, hexagonal
architecture package layout (domain/application/adapter/config), health
endpoint with integration test. Originally planned for Spring Boot 4.0
but pivoted due to massive package reorganization in 4.0 (see addenda
in research and plan docs).

Frontend: Vue 3 scaffolded via create-vue with TypeScript, Vue Router,
Vitest, ESLint, Prettier. Pivoted from Svelte due to ecosystem maturity
concerns (broken router ecosystem for Svelte 5).

Also: extended .gitignore for Java/Maven and Node/Vue artifacts, updated
CLAUDE.md with tech stack, build commands, agent documentation sections,
and document integrity rule.

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

frontend/src/components/HelloWorld.vue

@@ -0,0 +1,41 @@
+<script setup lang="ts">
+defineProps<{
+  msg: string
+}>()
+</script>
+
+<template>
+  <div class="greetings">
+    <h1 class="green">{{ msg }}</h1>
+    <h3>
+      You’ve successfully created a project with
+      <a href="https://vite.dev/" target="_blank" rel="noopener">Vite</a> +
+      <a href="https://vuejs.org/" target="_blank" rel="noopener">Vue 3</a>. What's next?
+    </h3>
+  </div>
+</template>
+
+<style scoped>
+h1 {
+  font-weight: 500;
+  font-size: 2.6rem;
+  position: relative;
+  top: -10px;
+}
+
+h3 {
+  font-size: 1.2rem;
+}
+
+.greetings h1,
+.greetings h3 {
+  text-align: center;
+}
+
+@media (min-width: 1024px) {
+  .greetings h1,
+  .greetings h3 {
+    text-align: left;
+  }
+}
+</style>