feat(frontend): Vue 3 + wa-sqlite + sync engine + auth + layouts

- package.json with Vue 3, Pinia, vue-router, wa-sqlite, Tailwind CSS 4, Vite
- wa-sqlite database layer with IDBBatchAtomicVFS (offline-first)
- Full schema mirroring backend tables (vehicles, orders, invoices, etc.)
- SyncEngine: fullSync, incrementalSync, pushQueue for offline queue
- Auth store with JWT parsing, login/register, plan tier detection
- Router with all routes and auth navigation guards
- AppLayout (sidebar desktop / bottom nav mobile) + AuthLayout
- Login/Register views connected to API contract
- SyncIndicator component (online/offline status)
- Reactive SQL query composable (useSqlQuery)
- Placeholder views for dashboard, orders, vehicles, appointments, catalog, settings

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

frontend/src/App.vue

@@ -0,0 +1,17 @@
+<template>
+  <component :is="layout">
+    <router-view />
+  </component>
+</template>
+
+<script setup>
+import { computed } from 'vue'
+import { useRoute } from 'vue-router'
+import AppLayout from './layouts/AppLayout.vue'
+import AuthLayout from './layouts/AuthLayout.vue'
+
+const route = useRoute()
+
+const layouts = { app: AppLayout, auth: AuthLayout }
+const layout = computed(() => layouts[route.meta.layout] || AppLayout)
+</script>