[refactor] Extract executionErrorStore from executionStore (#9060)

## Summary
Extracts error-related state and logic from `executionStore` into a
dedicated `executionErrorStore` for better separation of concerns.

## Changes
- **New store**: `executionErrorStore` with all error state
(`lastNodeErrors`, `lastExecutionError`, `lastPromptError`), computed
properties (`hasAnyError`, `totalErrorCount`,
`activeGraphErrorNodeIds`), and UI state (`isErrorOverlayOpen`,
`showErrorOverlay`, `dismissErrorOverlay`)
- **Moved util**: `executionIdToNodeLocatorId` extracted to
`graphTraversalUtil`, reusing `traverseSubgraphPath` and accepting
`rootGraph` as parameter
- **Updated consumers**: 12 files updated to import from
`executionErrorStore`
- **Backward compat**: Deprecated getters retained in `ComfyApp` for
extension compatibility

## Review Focus
- Deprecated getters in `app.ts` — can be removed in a future
breaking-change PR once extension authors migrate

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-9060-refactor-Extract-executionErrorStore-from-executionStore-30e6d73d36508101973de835ab6b199f)
by [Unito](https://www.unito.io)

src/components/graph/GraphCanvas.vue

@@ -70,7 +70,7 @@
       :key="nodeData.id"
       :node-data="nodeData"
       :error="
-        executionStore.lastExecutionError?.node_id === nodeData.id
+        executionErrorStore.lastExecutionError?.node_id === nodeData.id
           ? 'Execution error'
           : null
       "
@@ -170,6 +170,7 @@ import { storeToRefs } from 'pinia'
 import { useBootstrapStore } from '@/stores/bootstrapStore'
 import { useCommandStore } from '@/stores/commandStore'
 import { useExecutionStore } from '@/stores/executionStore'
+import { useExecutionErrorStore } from '@/stores/executionErrorStore'
 import { useNodeDefStore } from '@/stores/nodeDefStore'
 import { useColorPaletteStore } from '@/stores/workspace/colorPaletteStore'
 import { useSearchBoxStore } from '@/stores/workspace/searchBoxStore'
@@ -196,6 +197,7 @@ const workspaceStore = useWorkspaceStore()
 const canvasStore = useCanvasStore()
 const workflowStore = useWorkflowStore()
 const executionStore = useExecutionStore()
+const executionErrorStore = useExecutionErrorStore()
 const toastStore = useToastStore()
 const colorPaletteStore = useColorPaletteStore()
 const colorPaletteService = useColorPaletteService()
@@ -376,7 +378,7 @@ watch(
 // Update node slot errors for LiteGraph nodes
 // (Vue nodes read from store directly)
 watch(
-  () => executionStore.lastNodeErrors,
+  () => executionErrorStore.lastNodeErrors,
   (lastNodeErrors) => {
     if (!comfyApp.graph) return