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()

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

* fix unit tests

* move beforeLoadNewGraph to before graph is cleaned

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

src/scripts/ui.ts

@@ -634,7 +634,6 @@ export class ComfyUI {
               confirm('Clear workflow?')
             ) {
               app.clean()
-              app.graph.clear()
               useLitegraphService().resetView()
               api.dispatchCustomEvent('graphCleared')
             }