Document and unify pre-commit hooks for Python and JavaScript

[vgeorge]

Problem

The project's pre-commit setup is not documented, causing confusion and CI failures (e.g., in PR #906). Checks are not enforced locally for all contributors.

Suggested Solution

1. Unify Hooks: Extend the existing .pre-commit-config.yaml to include JavaScript checks (ESLint, Prettier) alongside the Python checks (Ruff).
2. Document Setup: Create a CONTRIBUTING.md or update DEVELOP.md to instruct contributors on how to install and use the hooks with uv run pre-commit install.

[kylebarron]

Indeed we should add a section in DEVELOP.md suggesting to use uv run pre-commit install to install pre-commit hooks locally.

1. Unify Hooks: Extend the existing .pre-commit-config.yaml to include JavaScript checks (ESLint, Prettier) alongside the Python checks (Ruff).

Pre-commit is a fully "static" lint approach, meaning that it has access to your code, but no dependencies. Pre-commit runs in isolated environments with only your code and the thing being run in that step.

This is why on the Python side, code format and linting is applied but not type checking, because that needs access to installed dependencies to work correctly.

We could probably add TS code formatting to pre-commit, but I assume we'd run into the same issue for type checking in TS that we do in Python.

Pre-commit is meant as an easy way to do a limited number of static checks, not all checks that might be run on CI