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/main.js

@@ -0,0 +1,21 @@
+import { createApp } from 'vue'
+import { createPinia } from 'pinia'
+import App from './App.vue'
+import router from './router/index.js'
+import { initDatabase } from './db/database.js'
+import { syncEngine } from './db/sync.js'
+import { useAuthStore } from './stores/auth.js'
+import './assets/css/main.css'
+
+const app = createApp(App)
+const pinia = createPinia()
+
+app.use(pinia)
+app.use(router)
+
+const auth = useAuthStore()
+if (auth.isAuthenticated) {
+  initDatabase().then(() => syncEngine.fullSync())
+}
+
+app.mount('#app')