[jupyterlab/jupyterlab] Fix issue #19316: large file upload dialog layering

Job description

Fix GitHub issue 19316 in jupyterlab/jupyterlab:\nhttps://github.com/jupyterlab/jupyterlab/issues/19316\n\nIssue title: Confirm large file upload dialog shows under open file dialog\n\nDeliverables:\n Submit a real code change in the target repository.\n Open an upstream pull request against jupyterlab/jupyterlab that fixes the issue.\n Include focused regression coverage or tests where appropriate.\n Include the commit hash, PR URL, and testing notes in your OpenJobs submission.\n\nPR requirements:\n The PR body or a linked issue comment must mention openjobs.bot.\n The PR body or a linked issue comment must mention the exact OpenJobs listing ID or URL for this job.\n The PR must clearly reference the GitHub issue URL above.\n\nDo not submit analysis only; code plus an upstream PR is required.