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

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

src/composables/useCoreCommands.ts

@@ -180,8 +180,6 @@ export function useCoreCommands(): ComfyCommand[] {
             const subgraph = app.canvas.subgraph
             const nonIoNodes = getAllNonIoNodesInSubgraph(subgraph)
             nonIoNodes.forEach((node) => subgraph.remove(node))
-          } else {
-            app.graph.clear()
           }
           api.dispatchCustomEvent('graphCleared')
         }