Fix string mismatch in unknown product error handling

Updated the unknown product name from "Unknown Product" to "One or more
products" to match the string value used in the error message view's
comparison logic.

This ensures the generic error message ("A product in the cart is no
longer available.") displays correctly instead of incorrectly using the
format string with "Unknown Product" as the product name.

Also updated test expectations to match the new string value.

Author: joshheald

Modules/Sources/Yosemite/Tools/POS/POSOrderService.swift

@@ -258,7 +258,7 @@ private extension POSOrderService {
         )
         static let unknownProductName = NSLocalizedString(
             "pointOfSale.orderController.unknownProduct",
-            value: "Unknown Product",
+            value: "One or more products",
             comment: "Fallback name for a product that couldn't be identified in error handling."
         )
     }

Modules/Tests/YosemiteTests/Tools/POS/POSOrderServiceTests.swift

@@ -362,7 +362,7 @@ struct POSOrderServiceTests {
                 #expect(missingItems.count == 1)
                 #expect(missingItems.first?.productID == 0) // Generic error
                 #expect(missingItems.first?.variationID == 0)
-                #expect(missingItems.first?.name == "Unknown Product")
+                #expect(missingItems.first?.name == "One or more products")
                 return true
             }
             return false
@@ -502,7 +502,7 @@ struct POSOrderServiceTests {
                 #expect(missingItems.count == 1)
                 #expect(missingItems.first?.productID == 0)
                 #expect(missingItems.first?.variationID == 999)
-                #expect(missingItems.first?.name == "Unknown Product")
+                #expect(missingItems.first?.name == "One or more products")
                 return true
             }
             return false