feat: printer duplicate copies setting (Feature 1)

- Add `duplicates` column (0-9) to printers table via migration
- Print loop repeats job 1+duplicates times per printer zone
- PrinterForm in Settings > Print now has ΑΝΤΙΓΡΑΦΑ (0-9) field
- PrinterRow shows amber badge when duplicates > 0

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

local_backend/services/printer_service.py

@@ -1256,10 +1256,12 @@ def _do_route_and_print(order_id: int, item_ids: List[int], db: Session) -> List
 
         success = False
         error_msg = None
+        copies = 1 + max(0, printer.duplicates or 0)
         try:
-            p = _get_printer(printer.ip_address, printer.port)
-            _print_kitchen_ticket(p, order, zone_items, db, printer.line_width)
-            p.close()
+            for _ in range(copies):
+                p = _get_printer(printer.ip_address, printer.port)
+                _print_kitchen_ticket(p, order, zone_items, db, printer.line_width)
+                p.close()
             success = True
             for item in zone_items:
                 item.printed = True