fix(#248): increase tree-node indent from 12px to 16px for better scanability

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/admin/tags/TagTreeNode.svelte

@@ -27,7 +27,8 @@ function toggleCollapse() {
 </script>
 
 <li role="treeitem" aria-selected={isActive} aria-expanded={hasChildren ? !isCollapsed : undefined}>
-	<div class="flex items-center" style="padding-left: {depth * 12}px">
+	<!-- 16px per level matches standard tree-view spacing and is large enough to be scannable -->
+	<div class="flex items-center" style="padding-left: {depth * 16}px">
 		{#if hasChildren}
 			<button
 				onclick={toggleCollapse}