Add nbstripout + pre-commit hook to standardize Jupyter notebook commits

[ty-fi]

Problem
Notebook commits currently include execution outputs and transient metadata, which creates noisy diffs and frequent merge conflicts.

Proposal
Adopt nbstripout via pre-commit so .ipynb files are automatically stripped before commit.

Impact

• Cleaner PR diffs focused on meaningful notebook source changes
• Fewer notebook merge conflicts
• Smaller/cleaner git history over time

Scope / tasks

• Add/update .pre-commit-config.yaml with an nbstripout hook for *.ipynb
• Add contributor setup docs (pre-commit install, optional pre-commit run --all-files)
• (Optional) add CI enforcement so unstripped notebooks fail checks
• (Optional) run a one-time normalization pass on existing notebooks

Acceptance criteria

• Committed notebooks do not include cell outputs/transient metadata
• Setup steps are documented and reproducible
• (If CI added) PR checks fail when notebook outputs are present

[ty-fi]

AI-written implementation notes below:

I think this should be treated as contributor/repository workflow setup, not core ReEDS runtime setup. Since pre-commit runs as a Git hook at commit time, we can install and invoke it via uv, but it is still somewhat outside the normal uv run python ... workflow.

Suggested approach:

• manage pre-commit as a dev dependency in the UV-managed environment
• document setup with:
  • uv sync
  • uv run pre-commit install
  • uv run pre-commit run --all-files
• use nbstripout in .pre-commit-config.yaml so staged .ipynb files are automatically stripped before commit
• optionally add CI enforcement later so PRs fail if notebooks still contain outputs/transient metadata

For documentation, I’d split this between README and CONTRIBUTING:

• README.md: brief contributor pointer, e.g. “See CONTRIBUTING.md for development setup, repository hooks, and contribution workflow.”
• CONTRIBUTING.md: the actual instructions for repo interaction, including:
  • installing dev dependencies
  • installing Git hooks
  • running hooks manually
  • notebook-specific expectations

That keeps “how to run ReEDS” separate from “how to interact with the repo cleanly as a contributor,” which feels like the right distinction for this change.