test: add Playwright regression test for high-res image preview overflow fix in ResultGallery

## Background

PR #10129 fixed a bug where high-resolution image previews overflowed the screen and hid the close button in the `ResultGallery` component (`src/components/sidebar/tabs/queue/ResultGallery.vue`).

As a follow-up, a Playwright end-to-end regression test should be added to prevent regressions of this fix.

## Task

Add a visual or functional Playwright test under `browser_tests/` that:
- Opens the result gallery with a high-resolution image
- Asserts that the image does not overflow the viewport (i.e., stays within `max-h-[90vh]` / `max-w-[90vw]` bounds)
- Asserts that the close button (`.p-galleria-close-button`) is visible and not hidden behind the image

## References

- Fix PR: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10129
- Review comment: https://github.com/Comfy-Org/ComfyUI_frontend/pull/10129#discussion_r2944106470

Requested by @DrJKL.

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-10130-test-add-Playwright-regression-test-for-high-res-image-preview-overflow-fix-in-Resul-3266d73d3650811c9034db0af5c3c6ec) by [Unito](https://www.unito.io)