Clean up tests introduced in PR #10532 (nested subgraph packing)

## Summary

PR #10532 (https://github.com/Comfy-Org/ComfyUI_frontend/pull/10532) introduced two new test files to cover the `_repointAncestorPromotions` / nested-subgraph-packing fix. A follow-up cleanup pass is needed on both files.

## Files to clean up

### 1. `src/lib/litegraph/src/LGraph.repointAncestorPromotions.test.ts`

- Dynamic node-type registration and cleanup is verbose; consider extracting a shared helper or test-fixture function.
- Three test cases share significant setup boilerplate (Pinia init, fixture state, type registration) that could be consolidated into a `beforeEach` or factory helper.
- Assertion style could be made more consistent across the three cases.

### 2. `browser_tests/tests/subgraphNestedPackValues.spec.ts`

- The two tests duplicate the load → enter → disable-Vue-nodes → select-all → `convertToSubgraph` → exit flow; extract into a shared helper.
- The `evaluate` block that filters `proxyWidgets` and resolves node IDs is complex inline browser JS; move logic into a well-named page-object method or helper.
- The `toPass` retry block (5 s timeout) wraps multiple assertions; consider splitting into focused individual retryable checks.
- Role-based locator strategy (`getByRole('textbox', { name: 'prompt' })`) introduced in the latest commit is good — ensure all other widget locators follow the same pattern instead of using positional selectors.
- Remove any leftover `console.log` / debug statements before merging cleanup.

## Requested by

@DrJKL in https://github.com/Comfy-Org/ComfyUI_frontend/pull/10532

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10532

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