Implement selection state management in Vue Nodes (#5421)

* let canvas continue to own selection state management

* fix merge error

* refactor: use computed instead of watcher for selectedNodeIds

Replace watcher pattern with computed for better Vue idioms:
- More reactive and efficient
- Automatically recomputes when dependencies change
- Simpler, more declarative code

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: improve injection error handling for selectedNodeIds

Replace silent fallback with explicit error when SelectedNodeIds
is not provided:
- Fail fast instead of silently using empty Set
- Clear error message for debugging
- Prevents nodes appearing unselected due to missing provider

Addresses DrJKL's concern about injection default behavior.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* test: improve mocking patterns using vi.mockObject

Replace manual mock interfaces with vi.mockObject for better type safety:
- Use Vitest's built-in mocking utilities instead of manual interfaces
- Properly configure mock return values
- Remove unnecessary type assertions

Addresses DrJKL's feedback on test mocking patterns.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* test: extract repeated nodeData for clarity

Extract common test nodeData object to reduce duplication:
- Move repeated VueNodeData object to describe scope
- Replace 6 instances of identical nodeData declarations
- Maintain different nodeData for specific test cases

Addresses DrJKL's suggestion to extract repeated test data.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* add type safety to mocks

---------

Co-authored-by: Claude <noreply@anthropic.com>

src/components/graph/GraphCanvas.vue

@@ -44,7 +44,6 @@
       :node-data="nodeData"
       :position="nodePositions.get(nodeData.id)"
       :size="nodeSizes.get(nodeData.id)"
-      :selected="nodeData.selected"
       :readonly="false"
       :executing="executionStore.executingNodeId === nodeData.id"
       :error="
@@ -79,6 +78,7 @@ import {
   computed,
   onMounted,
   onUnmounted,
+  provide,
   ref,
   shallowRef,
   watch,
@@ -112,6 +112,7 @@ import { useWorkflowPersistence } from '@/composables/useWorkflowPersistence'
 import { CORE_SETTINGS } from '@/constants/coreSettings'
 import { i18n, t } from '@/i18n'
 import type { LGraphNode } from '@/lib/litegraph/src/litegraph'
+import { SelectedNodeIdsKey } from '@/renderer/core/canvas/injectionKeys'
 import TransformPane from '@/renderer/core/layout/TransformPane.vue'
 import MiniMap from '@/renderer/extensions/minimap/MiniMap.vue'
 import VueGraphNode from '@/renderer/extensions/vueNodes/components/LGraphNode.vue'
@@ -189,6 +190,17 @@ const handleNodeSelect = nodeEventHandlers.handleNodeSelect
 const handleNodeCollapse = nodeEventHandlers.handleNodeCollapse
 const handleNodeTitleUpdate = nodeEventHandlers.handleNodeTitleUpdate
 
+// Provide selection state to all Vue nodes
+const selectedNodeIds = computed(
+  () =>
+    new Set(
+      canvasStore.selectedItems
+        .filter((item) => item.id !== undefined)
+        .map((item) => String(item.id))
+    )
+)
+provide(SelectedNodeIdsKey, selectedNodeIds)
+
 watchEffect(() => {
   nodeDefStore.showDeprecated = settingStore.get('Comfy.Node.ShowDeprecated')
 })