Add CI to enforce clean notebook outputs and metadata

[Nancy-Chauhan]

Summary

• Adds a GitHub Actions workflow that runs jupyter nbconvert to strip notebook outputs and metadata, and fails the check if any notebooks are dirty
• Adds a cleaning script (scripts/clean_tutorials_metadata_outputs.sh) for contributors to run locally
• Adds .gitignore for common Python/Node artifacts
• Posts a sticky PR comment with instructions when the check fails

Test plan

• Verified the cleaning script runs locally and correctly detects dirty notebooks
• Confirmed the workflow triggers on PRs touching python/, typescript/, or the workflow file itself

[github-actions]

Hey there!

We require our python tutorials to be stripped of outputs and metadata.

It seems your tutorials are not conforming to this standard. Please run:

./scripts/clean_tutorials_metadata_outputs.sh

from the root of the repo.