fix: suppress link rendering during slot sync after graph reconfigure (#8367)

## Description

Fixes link alignment issues after undo/redo operations in Vue Nodes 2.0.
When multiple connections exist from the same output to different nodes,
performing an undo would cause the connections to become misaligned with
their inputs.

## Root Cause

When undo triggers `loadGraphData`, the graph is reconfigured and Vue
node components are destroyed and recreated. The new slot elements mount
and schedule RAF-batched position syncs via `scheduleSlotLayoutSync`.
However, links are drawn **before** the RAF batch completes, causing
`getSlotPosition()` to return stale/missing positions.

## Solution

- Export a new `flushPendingSlotLayoutSyncs()` function from
`useSlotElementTracking.ts`
- Create a `useGraphConfigureSlotSync` composable that flushes pending
syncs after graph configuration
- Integrate the flush into `addAfterConfigureHandler` in `app.ts`,
called after `onAfterGraphConfigured`
- Force canvas redraw after flushing to render links with correct
positions

## Testing

- Added unit tests for `flushPendingSlotLayoutSyncs`
- Added unit tests for `useGraphConfigureSlotSync` composable
- Manual verification: connections now align correctly after undo/redo
operations

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-8367-fix-flush-pending-slot-layout-syncs-after-graph-configure-2f66d73d365081a3a564fac96c44a048)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Subagent 5 <subagent@example.com>
Co-authored-by: Amp <amp@ampcode.com>

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

@@ -12,6 +12,7 @@ import { useSharedCanvasPositionConversion } from '@/composables/element/useCanv
 import { LiteGraph } from '@/lib/litegraph/src/litegraph'
 import { getSlotKey } from '@/renderer/core/layout/slots/slotIdentifier'
 import { layoutStore } from '@/renderer/core/layout/store/layoutStore'
+import { app } from '@/scripts/app'
 import type { SlotLayout } from '@/renderer/core/layout/types'
 import {
   isPointEqual,
@@ -28,16 +29,36 @@ const raf = createRafBatch(() => {
 
 function scheduleSlotLayoutSync(nodeId: string) {
   pendingNodes.add(nodeId)
+  // Re-assert pending flag for late mounts (Vue components mounting after
+  // flushScheduledSlotLayoutSync was called synchronously in onConfigure)
+  layoutStore.setPendingSlotSync(true)
   raf.schedule()
 }
 
-function flushScheduledSlotLayoutSync() {
-  if (pendingNodes.size === 0) return
+export function flushScheduledSlotLayoutSync() {
+  if (pendingNodes.size === 0) {
+    // No pending nodes - check if we should wait for Vue components to mount
+    const graph = app.canvas?.graph
+    const hasNodes = graph && graph._nodes && graph._nodes.length > 0
+    if (hasNodes) {
+      // Graph has nodes but Vue hasn't mounted them yet - keep flag set
+      // so late mounts can re-assert it via scheduleSlotLayoutSync()
+      return
+    }
+    // No nodes in graph - safe to clear the flag (no Vue components will mount)
+    layoutStore.setPendingSlotSync(false)
+    app.canvas?.setDirty(true, true)
+    return
+  }
   const conv = useSharedCanvasPositionConversion()
   for (const nodeId of Array.from(pendingNodes)) {
     pendingNodes.delete(nodeId)
     syncNodeSlotLayoutsFromDOM(nodeId, conv)
   }
+  // Clear the pending sync flag - slots are now synced
+  layoutStore.setPendingSlotSync(false)
+  // Trigger canvas redraw now that links can render with correct positions
+  app.canvas?.setDirty(true, true)
 }
 
 export function syncNodeSlotLayoutsFromDOM(