fix: add z-index property to the divider element to establish proper stacking order (#17)

Co-authored-by: Copilot <[email protected]>

Author: rijkvanzanten

packages/vue-split-panel/src/SplitPanel.vue

@@ -339,6 +339,7 @@ defineExpose({ collapse, expand, toggle });
 
 .divider {
 	position: relative;
+	z-index: 1;
 
 	&:not(.disabled) {
 		& :deep(> :first-child) {