fix mmb navigation when click starts on Vue nodes (#5921)

## Summary

Fixes https://github.com/Comfy-Org/ComfyUI_frontend/issues/5860
by updating Vue node pointer interactions to forward middle mouse button
events to canvas instead of handling them locally.

## Review Focus

Middle mouse button event detection logic using both `button` property
and `buttons` bitmask for cross-browser compatibility. Test coverage for
pointer event forwarding behavior.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5921-fix-mmb-navigation-when-click-starts-on-Vue-nodes-2826d73d3650819688eec4600666755d)
by [Unito](https://www.unito.io)

---------

Co-authored-by: DrJKL <DrJKL@users.noreply.github.com>

src/renderer/extensions/vueNodes/composables/useNodePointerInteractions.ts

@@ -1,5 +1,6 @@
 import { type MaybeRefOrGetter, computed, onUnmounted, ref, toValue } from 'vue'
 
+import { isMiddlePointerInput } from '@/base/pointerUtils'
 import type { VueNodeData } from '@/composables/graph/useGraphNodeManager'
 import { useCanvasInteractions } from '@/renderer/core/canvas/useCanvasInteractions'
 import { layoutStore } from '@/renderer/core/layout/store/layoutStore'
@@ -34,6 +35,12 @@ export function useNodePointerInteractions(
   const { forwardEventToCanvas, shouldHandleNodePointerEvents } =
     useCanvasInteractions()
 
+  const forwardMiddlePointerIfNeeded = (event: PointerEvent) => {
+    if (!isMiddlePointerInput(event)) return false
+    forwardEventToCanvas(event)
+    return true
+  }
+
   // Drag state for styling
   const isDragging = ref(false)
   const dragStyle = computed(() => {
@@ -52,6 +59,8 @@ export function useNodePointerInteractions(
       return
     }
 
+    if (forwardMiddlePointerIfNeeded(event)) return
+
     const stopNodeDragTarget =
       event.target instanceof HTMLElement
         ? event.target.closest('[data-capture-node="true"]')
@@ -90,6 +99,8 @@ export function useNodePointerInteractions(
   }
 
   const handlePointerMove = (event: PointerEvent) => {
+    if (forwardMiddlePointerIfNeeded(event)) return
+
     if (isDragging.value) {
       void handleDrag(event)
     }
@@ -129,6 +140,8 @@ export function useNodePointerInteractions(
   }
 
   const handlePointerUp = (event: PointerEvent) => {
+    if (forwardMiddlePointerIfNeeded(event)) return
+
     if (isDragging.value) {
       handleDragTermination(event, 'drag end')
     }