fix: suppress link rendering during slot sync after graph reconfigure

After graph reconfiguration (e.g., undo/redo), there's a timing gap where
canvas renders links before Vue components have mounted and synced slot
positions to layoutStore.

This adds a pendingSlotSync flag to layoutStore that:
- Is set to true at start of graph.onConfigure()
- Is cleared after flushScheduledSlotLayoutSync() completes
- Causes drawConnections() to skip link rendering when true

This prevents links from rendering with stale/missing positions during the
brief window between configure() completing and Vue components syncing.

Amp-Thread-ID: https://ampcode.com/threads/T-019c084c-49dd-764b-8125-8938c42612c8
Co-authored-by: Amp <amp@ampcode.com>

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

@@ -31,13 +31,19 @@ function scheduleSlotLayoutSync(nodeId: string) {
   raf.schedule()
 }
 
-function flushScheduledSlotLayoutSync() {
-  if (pendingNodes.size === 0) return
+export function flushScheduledSlotLayoutSync() {
+  if (pendingNodes.size === 0) {
+    // Even if no pending nodes, clear the flag (e.g., graph with no nodes)
+    layoutStore.setPendingSlotSync(false)
+    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)
 }
 
 export function syncNodeSlotLayoutsFromDOM(