Add schedule preview dropdown styles and various improvements

- Add .schedule-preview-dropdown and .schedule-preview-item CSS classes
- Add .btn-schedule-preview badge styling
- Add preview functionality for entity list views
- Improve modal and dropdown styling
- Various JS and SCSS enhancements

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sources/scss/components/_groups.scss

@@ -954,6 +954,20 @@
             color: $es-primary;
         }
 
+        // Country holidays variant - use calendar icon style
+        &.country-holidays {
+            background: rgba(139, 92, 246, 0.1);
+            color: #8b5cf6;
+
+            &:hover {
+                background: rgba(139, 92, 246, 0.2);
+            }
+
+            &.clickable {
+                background: rgba(139, 92, 246, 0.15);
+            }
+        }
+
         i {
             font-size: 10px;
         }