refactor: move setupSettings into SettingsHelper

## Summary

Tests in `browser_tests/tests/resultGallery.spec.ts` (and likely other test files) call `comfyPage.settings.setSetting()` multiple times in a `beforeEach` block to configure required settings. This pattern should be encapsulated into a dedicated `setupSettings` method on the `SettingsHelper` class so tests can invoke it in a single, readable call.

## Motivation

- Reduces boilerplate in test `beforeEach` hooks
- Centralises common setting configurations, making them easier to maintain
- Improves readability and consistency across the test suite

## References

- PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10134
- Comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10134#discussion_r2950107456

/cc @DrJKL

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