live selection (#7465)

## Summary

Add real-time selection feedback during marquee drag, matching the
behavior users expect from other applications.

## Changes

- Nodes and groups are now selected/deselected instantly as the
selection rectangle moves
- Supports all modifier keys (Shift to add, Alt to subtract) during drag
- Added Comfy.Graph.LiveSelection setting (off by default)

## Rationale

This interaction pattern is standard across virtually all design and
productivity software:
- Operating Systems: Windows Explorer, macOS Finder, and Linux file
managers all show live selection feedback when dragging
- Design Tools: Figma, Sketch, Adobe Illustrator, Photoshop, and Blender
use real-time selection
- IDEs: VS Code, JetBrains IDEs show live selection in file explorers
- Node Editors: Unreal Engine Blueprints, Unity Shader Graph, and
Houdini all support live selection

## Screenshots

https://github.com/user-attachments/assets/8b0c2217-47f9-4422-9cab-cb39e145310c

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-7465-live-selection-2c96d73d36508133a4a6f917955d55b3)
by [Unito](https://www.unito.io)

src/platform/settings/composables/useLitegraphSettings.ts

@@ -93,6 +93,12 @@ export const useLitegraphSettings = () => {
     if (canvas) canvas.dragZoomEnabled = dragZoomEnabled
   })
 
+  watchEffect(() => {
+    const liveSelection = settingStore.get('Comfy.Graph.LiveSelection')
+    const { canvas } = canvasStore
+    if (canvas) canvas.liveSelection = liveSelection
+  })
+
   watchEffect(() => {
     CanvasPointer.doubleClickTime = settingStore.get(
       'Comfy.Pointer.DoubleClickTime'