feat: scaffold Vue 3 + Vuetify + Pinia frontend themed to FabledDesignSystem

Curator signature accent (#A87338, aged amber) is baked into
fabled-tokens.js. Vuetify theme consumes the same tokens module the rest
of the SPA does, so updating design system tokens propagates throughout.
Vite dev server proxies /api and /ws to the Quart backend.

App.vue references AppShell (lands in Task 9) and main.js references
router.js (lands in Task 9) — these are intentionally split so Task 8 is
the framework scaffold and Task 9 is the navigation/shell content.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/App.vue

@@ -0,0 +1,11 @@
+<template>
+  <v-app>
+    <AppShell>
+      <RouterView />
+    </AppShell>
+  </v-app>
+</template>
+
+<script setup>
+import AppShell from './components/AppShell.vue'
+</script>