feat: scaffold Nuxt 3 + Nuxt UI 3

Initialize Nuxt 4 project with @nuxt/ui template including Tailwind CSS v4,
TypeScript, ESLint, and Nuxt UI v3 (via @nuxt/ui package).

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

front-end/app/app.config.ts

@@ -0,0 +1,8 @@
+export default defineAppConfig({
+  ui: {
+    colors: {
+      primary: 'green',
+      neutral: 'slate'
+    }
+  }
+})