chore: initial commit

Vue 3 + Tailwind v4 frontend scaffold with living design system
at /design. Pinned dependencies, dev-only a11y toolbar with
colour-vision simulation, WCAG contrast checker, and axe-core audit.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/App.vue

@@ -0,0 +1,21 @@
+<script setup>
+import { computed, defineAsyncComponent } from 'vue'
+import { useRoute } from 'vue-router'
+import DefaultLayout from './layouts/DefaultLayout.vue'
+
+const route = useRoute()
+const useDefaultLayout = computed(() => route.meta.layout !== 'none')
+
+const isDev = import.meta.env.DEV
+const A11yToolbar = isDev
+  ? defineAsyncComponent(() => import('./design-system/devtools/A11yToolbar.vue'))
+  : null
+</script>
+
+<template>
+  <DefaultLayout v-if="useDefaultLayout">
+    <router-view />
+  </DefaultLayout>
+  <router-view v-else />
+  <A11yToolbar v-if="isDev" />
+</template>