Enhance product management and coupon features

- Added styling for input group add-ons and additional fields in SCSS.
- Updated shop coupon view to include a new column for usage count.
- Display coupon code and amount in order details if applicable.
- Improved product edit template to handle custom fields with required validation.
- Modified product save logic to include custom field requirements.
- Enhanced decimal normalization function for better input handling.
- Implemented checkbox normalization for form submissions.
- Updated custom fields in product templates to reflect required status.
- Fixed URL for fetching changelog updates.

admin/templates/shop-order/order-details.php

@@ -44,6 +44,9 @@ ob_start();
         <div class="panel">
           <div class="panel-body">
             <div>Kwota zamówienia <b><?= $this -> order[ 'summary' ];?> zł</b></div>
+            <? if ( $this -> coupon ):?>
+              <div>Kod rabatowy: <span style="color: #cc0000;"><?= $this -> coupon -> name;?> - <?= $this -> coupon -> amount;?> <?= $this -> coupon -> type == 1 ? '%' : 'zł';?></span></div>
+            <? endif;?>
             <br>
             <div><?= strip_tags( $this -> order[ 'transport' ] );?>: <b><?= $this -> order[ 'transport_cost' ];?> zł</b></div>
             <? if ( $this -> order['transport_id'] == 2 and $this -> order[ 'inpost_paczkomat' ] ):?>