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/__tests__/HelloWorld.spec.ts

@@ -0,0 +1,11 @@
+import { describe, it, expect } from 'vitest'
+
+import { mount } from '@vue/test-utils'
+import HelloWorld from '../HelloWorld.vue'
+
+describe('HelloWorld', () => {
+  it('renders properly', () => {
+    const wrapper = mount(HelloWorld, { props: { msg: 'Hello Vitest' } })
+    expect(wrapper.text()).toContain('Hello Vitest')
+  })
+})