Add data import export functions

public/app.js

@@ -113,7 +113,7 @@ function switchView(viewName) {
   document.querySelectorAll('.view').forEach((view) => view.classList.toggle('active-view', view.id === `${viewName}-view`));
   document.querySelectorAll('.nav-item').forEach((item) => item.classList.toggle('active', item.dataset.view === viewName));
   $('#new-customer-button').hidden = viewName === 'customers' || viewName === 'vehicles' || viewName === 'orders';
-  $('#page-title').textContent = viewName === 'overview' ? 'Good morning, workshop.' : viewName === 'customers' ? 'Your customer directory.' : viewName === 'vehicles' ? 'Know every vehicle.' : viewName === 'orders' ? 'Keep the bays moving.' : 'Manage workshop access.';
+  $('#page-title').textContent = viewName === 'overview' ? 'Good morning, workshop.' : viewName === 'customers' ? 'Your customer directory.' : viewName === 'vehicles' ? 'Know every vehicle.' : viewName === 'orders' ? 'Keep the bays moving.' : viewName === 'users' ? 'Manage workshop access.' : 'Keep your workshop data portable.';
   if (viewName === 'customers') loadCustomers();
   if (viewName === 'vehicles') loadVehicles();
   if (viewName === 'orders') loadOrders();
@@ -137,6 +137,21 @@ $('#cancel-record-button').addEventListener('click', () => $('#record-dialog').c
 $('#close-record-button').addEventListener('click', () => $('#record-dialog').close());
 $('#order-filters').addEventListener('input', renderOrders);
 $('#order-filters').addEventListener('change', renderOrders);
+$('#export-data-button').addEventListener('click', async () => {
+  try {
+    const response = await fetch('/api/data/export');
+    if (!response.ok) throw new Error('Unable to export database data.');
+    const blob = await response.blob();
+    const link = document.createElement('a'); link.href = URL.createObjectURL(blob); link.download = `car-service-backup-${new Date().toISOString().slice(0, 10)}.json`; link.click(); URL.revokeObjectURL(link.href);
+    $('#notice').textContent = 'Database backup downloaded.';
+  } catch (error) { showError(error); }
+});
+$('#import-data-input').addEventListener('change', async (event) => {
+  const file = event.target.files[0]; if (!file) return;
+  $('#import-file-name').textContent = file.name;
+  if (!window.confirm('Importing a backup replaces all current database data. Continue?')) { event.target.value = ''; $('#import-file-name').textContent = 'No file selected.'; return; }
+  try { const result = await request('/api/data/import', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: await file.text() }); $('#notice').textContent = `Backup imported: ${result.imported} records restored.`; await loadOverview(); await loadCustomers(); await loadVehicles(); await loadOrders(); await loadUsers(); } catch (error) { showError(error); } finally { event.target.value = ''; }
+});
 ['vin', 'licensePlate'].forEach((name) => $('#record-form').elements[name].addEventListener('blur', async (event) => {
   const identifier = event.target.value.trim();
   if (!identifier) return;