Add z-index management in Vue Nodes based on interaction recency (#5429)

* fix z-index on selection for vue nodes

* fix unused export

* refactor to DDD

* Use Tailwind utility for pointer events instead of inline style

Move pointer-events: auto from inline style to Tailwind class
pointer-events-auto as suggested in PR review.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* Rename defaultSource to layoutSource parameter

Rename parameter in useNodeZIndex options interface for better
clarity as suggested in PR review.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* Improve test mocking pattern with vi.mocked approach

Replace global mock object with per-test vi.mocked pattern
and proper Partial typing instead of as any, as suggested
in PR review.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

* [auto-fix] Apply ESLint and Prettier fixes

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/renderer/extensions/vueNodes/components/LGraphNode.vue

@@ -22,13 +22,14 @@
           'border-red-500 bg-red-50': error,
           'will-change-transform': isDragging
         },
-        lodCssClass
+        lodCssClass,
+        'pointer-events-auto'
       )
     "
     :style="[
       {
         transform: `translate(${layoutPosition.x ?? position?.x ?? 0}px, ${(layoutPosition.y ?? position?.y ?? 0) - LiteGraph.NODE_TITLE_HEIGHT}px)`,
-        pointerEvents: 'auto'
+        zIndex: zIndex
       },
       dragStyle
     ]"
@@ -192,6 +193,7 @@ onErrorCaptured((error) => {
 // Use layout system for node position and dragging
 const {
   position: layoutPosition,
+  zIndex,
   startDrag,
   handleDrag: handleLayoutDrag,
   endDrag