feat: standardize invoice number field, refine invoice creation logic, and update module foreign key constraints

app/Helpers/OrderHelper.php

@@ -23,7 +23,7 @@ class OrderHelper
             $number = $prefix . '-' . strtoupper(Str::random(8));
 
             $exists = match ($prefix) {
-                'INV'   => Invoice::where('invoice_num', $number)->exists(),
+                'INV' => Invoice::where('invoice_number', $number)->exists(),
                 default => Order::where('order_num', $number)->exists(),
             };
         } while ($exists);