fix: onNodeRemoved not called when loading new graph (and tearing down previous) (#5407)

* standardize graph cleanup

* test: fix useCoreCommands tests and add regression test

- Fix mocking to properly simulate app.clean() calling graph.clear()
- Add intelligent subgraph detection in mock to match real implementation
- Add regression test for Vue node cleanup bug to prevent future regressions
- Ensures app.clean() properly triggers onNodeRemoved events through graph.clear()

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

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

* fix unit tests

* move beforeLoadNewGraph to before graph is cleaned

---------

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

tests-ui/tests/composables/useCoreCommands.test.ts

@@ -6,17 +6,25 @@ import { api } from '@/scripts/api'
 import { app } from '@/scripts/app'
 import { useSettingStore } from '@/stores/settingStore'
 
-vi.mock('@/scripts/app', () => ({
-  app: {
-    clean: vi.fn(),
-    canvas: {
-      subgraph: null
-    },
-    graph: {
-      clear: vi.fn()
+vi.mock('@/scripts/app', () => {
+  const mockGraphClear = vi.fn()
+  const mockCanvas = { subgraph: undefined }
+
+  return {
+    app: {
+      clean: vi.fn(() => {
+        // Simulate app.clean() calling graph.clear() only when not in subgraph
+        if (!mockCanvas.subgraph) {
+          mockGraphClear()
+        }
+      }),
+      canvas: mockCanvas,
+      graph: {
+        clear: mockGraphClear
+      }
     }
   }
-}))
+})
 
 vi.mock('@/scripts/api', () => ({
   api: {