Dashboard tweaks, add bulk /check-upcs endpoint for import validation

inventory-server/src/routes/import.js

@@ -1931,6 +1931,76 @@ router.post('/generate-upc', async (req, res) => {
   }
 });
 
+// Bulk "does this UPC already exist" check for the import validator.
+// The one-at-a-time alternative is /search-products?q=<upc>, but that runs a
+// five-column LIKE '%q%' scan across ten joined tables (~6s each) and every call
+// queues on the single shared connection from getDbConnection() — a 20-product
+// batch takes minutes. This answers the whole batch with one indexed IN() lookup
+// on idx_upc. Matches /check-upc-and-generate-sku's semantics: `upc` only, not upc_2.
+const MAX_UPCS_PER_CHECK = 500;
+
+router.get('/check-upcs', async (req, res) => {
+  const { upcs } = req.query;
+
+  if (!upcs) {
+    return res.status(400).json({ error: 'upcs query parameter is required' });
+  }
+
+  // Dedupe and keep only well-formed barcodes — anything else can't match the
+  // column anyway, and dropping it keeps the IN() list tight.
+  const upcList = [...new Set(
+    String(upcs).split(',').map(s => s.trim()).filter(s => /^\d{8,14}$/.test(s))
+  )];
+
+  if (upcList.length === 0) {
+    return res.json({ found: {}, checked: 0 });
+  }
+
+  if (upcList.length > MAX_UPCS_PER_CHECK) {
+    return res.status(400).json({
+      error: `Too many UPCs (${upcList.length}); send at most ${MAX_UPCS_PER_CHECK} per request`
+    });
+  }
+
+  try {
+    const { connection } = await getDbConnection();
+
+    const placeholders = upcList.map(() => '?').join(',');
+    const [rows] = await connection.query(
+      `SELECT pid, upc, itemnumber, description FROM products WHERE upc IN (${placeholders})`,
+      upcList
+    );
+
+    // idx_upc is non-unique, so a UPC can legitimately hit more than one product.
+    // Report the lowest pid (the original) and say how many share it.
+    const found = {};
+    for (const row of rows) {
+      const key = String(row.upc);
+      const existing = found[key];
+      if (!existing) {
+        found[key] = {
+          pid: row.pid,
+          itemNumber: row.itemnumber,
+          title: row.description,
+          matchCount: 1
+        };
+        continue;
+      }
+      existing.matchCount += 1;
+      if (row.pid < existing.pid) {
+        existing.pid = row.pid;
+        existing.itemNumber = row.itemnumber;
+        existing.title = row.description;
+      }
+    }
+
+    return res.json({ found, checked: upcList.length });
+  } catch (error) {
+    console.error('Error checking UPCs:', error);
+    return res.status(500).json({ error: 'Failed to check UPCs', details: error.message });
+  }
+});
+
 // Endpoint to check UPC and generate item number
 router.get('/check-upc-and-generate-sku', async (req, res) => {
   const { upc, supplierId } = req.query;