Add Siti Delivery Time Notices plugin and related functionality

- Create main plugin file with metadata and initialization logic.
- Implement SitiDeliveryTimeNotice class for managing delivery time settings.
- Add JavaScript for updating delivery time notices on product pages.
- Update GitHub Actions workflow to reflect new file structure.
- Remove deprecated master-file.php.

assets/js/levertijden.js

@@ -0,0 +1,41 @@
+(function ($) {
+	$(function () {
+		var $card = $('.lb-levertijd-card');
+		if (!$card.length) {
+			return;
+		}
+
+		var $text = $card.find('.lb-levertijd-text');
+		var defaultText = $card.data('defaultText') || '';
+		var $form = $('.variations_form');
+
+		function updateCard(text) {
+			if (!text) {
+				$card.toggleClass('lb-levertijd-hidden', true).hide();
+				return;
+			}
+
+			$text.text(text);
+			$card.toggleClass('lb-levertijd-hidden', false).show();
+		}
+
+		if (!$form.length) {
+			updateCard(defaultText);
+			return;
+		}
+
+		updateCard(defaultText);
+
+		$form.on('found_variation', function (event, variation) {
+			if (variation && variation.lb_levertijd) {
+				updateCard(variation.lb_levertijd);
+			} else {
+				updateCard(defaultText);
+			}
+		});
+
+		$form.on('reset_data hide_variation', function () {
+			updateCard(defaultText);
+		});
+	});
+}(jQuery));