Node ghost mode when adding nodes (#8694)

## Summary

Adds option for adding a node as a "ghost" that follows the cursor until
the user left clicks to confirm, or esc/right click to cancel.

## Changes

- **What**: 
Adds option for `ghost` when calling `graph.add`  
This adds the node with a `flag` of ghost which causes it to render
transparent
Selects the node, then sets the canvas as dragging to stick the node to
the cursor

## Screenshots (if applicable)



https://github.com/user-attachments/assets/dcb5702f-aba3-4983-aa40-c51f24a4767a

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8694-Node-ghost-mode-when-adding-nodes-2ff6d73d3650815591f2c28415050463)
by [Unito](https://www.unito.io)

src/components/graph/NodeTooltip.vue

@@ -61,7 +61,7 @@ async function showTooltip(tooltip: string | null | undefined) {
 function onIdle() {
   const { canvas } = comfyApp
   const node = canvas?.node_over
-  if (!node) return
+  if (!node || node.flags?.ghost) return
 
   const ctor = node.constructor as { title_mode?: 0 | 1 | 2 | 3 }
   const nodeDef = nodeDefStore.nodeDefsByName[node.type ?? '']