[BUG] Notebook structure CI succeeds without validating notebooks

The Notebook Quality Check runs scripts/validate_notebooks.py without any paths. The script validates only paths passed in argv; with no arguments it prints “No notebooks to validate” and exits 0. Thus notebook pull requests pass this structural check without checking empty cells or saved error outputs. Reproduce by running python scripts/validate_notebooks.py from the repository root: it exits successfully without examining notebooks. Expected: the workflow supplies the selected notebook paths or the script defaults to the intended notebook set.