feat: replace custom discount with absolute value in favor of percentage

tests/Form/Admin/Groups/AccommodationBookingTypeTest.php

@@ -74,13 +74,13 @@ class AccommodationBookingTypeTest extends TestCase
     }
 
     /**
-     * The label is printed verbatim on the customer's PDF, so a percentage without one is
+     * The label is printed verbatim on the customer's PDF, so an amount without one is
      * refused — and in the Default group, so that even a draft cannot store the pair half-set.
      */
     public function testTotalDiscountRequiresALabel(): void
     {
         $booking = new AccommodationBooking();
-        $booking->setTotalDiscount(5);
+        $booking->setTotalDiscountAmount(5000);
 
         $violations = $this->validate($booking, ['Default']);
 
@@ -91,17 +91,17 @@ class AccommodationBookingTypeTest extends TestCase
     public function testALabelledTotalDiscountPassesValidation(): void
     {
         $booking = new AccommodationBooking();
-        $booking->setTotalDiscount(5);
+        $booking->setTotalDiscountAmount(5000);
         $booking->setTotalDiscountLabel('Treuerabatt');
 
         self::assertCount(0, $this->validate($booking, ['Default']));
     }
 
     /**
-     * The reverse is harmless — without a percentage the label never reaches a breakdown row —
+     * The reverse is harmless — without an amount the label never reaches a breakdown row —
      * so it is deliberately left valid rather than blocking a half-typed edit.
      */
-    public function testALabelWithoutAPercentageIsAccepted(): void
+    public function testALabelWithoutAnAmountIsAccepted(): void
     {
         $booking = new AccommodationBooking();
         $booking->setTotalDiscountLabel('Treuerabatt');