fix: context menu appears at wrong position on first click after canvas move (#7821)

## Summary

Fixed context menu positioning bug where menu appeared below mouse
cursor on first right-click after moving canvas, causing viewport
overflow.

## Changes

Initialize lastScale/lastOffset* to current canvas transform values when
opening menu, preventing updateMenuPosition from overwriting PrimeVue's
flip-adjusted position on the first RAF tick.

## Review Focus

<!-- Critical design decisions or edge cases that need attention -->

<!-- If this PR fixes an issue, uncomment and update the line below -->
Fixes #7666 

## Screenshots (if applicable)

Please pay attention to the first right-click in each video — that’s
where the fix makes a difference.

**Before**


https://github.com/user-attachments/assets/29621621-a05e-414a-a4cc-5aa5a31b5041

**After**


https://github.com/user-attachments/assets/5f46aa69-97a0-44a4-9894-b205fe3d58ed

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7821-fix-context-menu-appears-at-wrong-position-on-first-click-after-canvas-move-2db6d73d365081e4a8ebc0d91e3f927b)
by [Unito](https://www.unito.io)

Co-authored-by: Alexander Brown <drjkl@comfy.org>

src/components/graph/NodeContextMenu.vue

@@ -220,6 +220,12 @@ function show(event: MouseEvent) {
     y: screenY / scale - offset[1]
   }
 
+  // Initialize last* values to current transform to prevent updateMenuPosition
+  // from overwriting PrimeVue's flip-adjusted position on the first RAF tick
+  lastScale = scale
+  lastOffsetX = offset[0]
+  lastOffsetY = offset[1]
+
   isOpen.value = true
   contextMenu.value?.show(event)
 }