perf: detect pointer drag in useTransformSettling for pan optimization (#9649)

## Summary

When many nodes are rendered in the transform container, both zoom and
pan can cause FPS drops because the browser re-rasterizes all visible
content at the new transform. `will-change: transform` tells the browser
to keep the layer as a GPU texture and skip re-rasterization during
active interaction, restoring visual quality only after settling.

- Add pointer drag detection so `will-change: transform` covers pan in
addition to zoom. Without this, dragging with 256+ nodes causes jank as
the browser re-rasterizes the entire layer on every frame of the pan.
- Fix settleDelay from 16ms to 256ms. At 16ms the debounce fires between
consecutive wheel events (~50ms apart on a physical mouse), causing
`will-change` to toggle on/off rapidly. Each toggle forces the browser
to promote/demote the compositor layer, which is more expensive than not
having the optimization at all.
- Replace scoped CSS with Tailwind `will-change-transform`.
- Remove per-node `will-change: transform` on `.lg-node`. Promoting each
node to its own compositor layer (256 nodes = 256 GPU textures)
increases memory pressure and compositing overhead, making performance
worse than a single promoted container.
- Previously, the virtual DOM of Nodes was updated during zooming and
dragging, but now this update is avoided through some techniques.
- Using the 3D versions of scale and translate can provide a smoother
experience when dealing with a large number of nodes.

## Test plan
- [x] Unit tests updated and passing
- [x] Manual: verify during both zoom and pan
- [x] Manual: compare pan FPS with 256 nodes before/after

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9649-perf-detect-pointer-drag-in-useTransformSettling-for-pan-optimization-31e6d73d3650818bb2c3ccd01a465140)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <github-actions@github.com>

packages/design-system/src/css/style.css

@@ -1420,15 +1420,6 @@ audio.comfy-audio.empty-audio-widget {
     font-size 0.1s ease;
 }
 
-/* Performance optimization during canvas interaction */
-.transform-pane--interacting .lg-node * {
-  transition: none !important;
-}
-
-.transform-pane--interacting .lg-node {
-  will-change: transform;
-}
-
 /* ===================== Mask Editor Styles ===================== */
 /* To be migrated to Tailwind later */
 #maskEditor_brush {