docs: add CONTRIBUTING.md

[ANANYA542]

Describe your changes

Adds docs/contributing/contributing.md — a concise contributor guide that walks a new contributor through the full workflow from fork to merged PR.
Covers: ways to contribute, environment setup (referencing existing README install instructions rather than duplicating them), all 13 pre-commit hooks documented, code standards, how to run the test suite locally using the exact CI commands, PR checklist, review process with CHANGELOG format, and a troubleshooting table.
The goal is to give new contributors a single document to reference rather than piecing together information from the README, PR template, and CI config separately. Redundant sections have been removed and replaced with direct references to existing docs.

Issue Link

fixes #406

Type of change

• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation (Addition or improvements to documentation)

Checklist before requesting a review

• My branch is up-to-date with the target branch - if not update your fork with the changes from the target branch (use pull with --rebase option if possible).
• [X ] I have performed a self-review of my code
• For any new/modified functions/classes I have added docstrings that clearly describe its purpose, expected inputs and returned values
• I have placed in-line comments to clarify the intent of any hard-to-understand passages of my code
• I have updated the README to cover introduced code changes
• I have added tests that prove my fix is effective or that my feature works
• I have given the PR a name that clearly describes the change, written in imperative form (context).
• I have requested a reviewer and an assignee (assignee is responsible for merging). This applies only if you have write access to the repo, otherwise feel free to tag a maintainer to add a reviewer and assignee.

Checklist for reviewers

Each PR comes with its own improvements and flaws. The reviewer should check the following:

• the code is readable
• the code is well tested
• the code is documented (including return types and parameters)
• the code is easy to maintain

Author checklist after completed review

• I have added a line to the CHANGELOG describing this change, in a section
  reflecting type of change (add section where missing):
  • added: when you have added new functionality
  • changed: when default behaviour of the code has been changed
  • fixes: when your contribution fixes a bug
  • maintenance: when your contribution is relates to repo maintenance, e.g. CI/CD or documentation

Checklist for assignee

• PR is up to date with the base branch
• the tests pass
• (if the PR is not just maintenance/bugfix) the PR is assigned to the next milestone. If it is not, propose it for a future milestone.
• author has added an entry to the changelog (and designated the change as added, changed, fixed or maintenance)
• Once the PR is ready to be merged, squash commits and merge the PR.

[sadamov]

@ANANYA542 I saw that you are expanding our work on this PR here. Note that autodoc is already tackled by #322. So I would prefer if this PR here could focus on the CONTRIBUTING.md file. And work closely together with #516 to reduce duplicated information that's hard to maintain. Could you reduce the scope of this PR here and update the title to make it clearer?

[ANANYA542]

@sadamov Thanks for the review! I have dropped the Jupyter Book commits since #322 already tackles autodoc, and reduced the scope to focus solely on CONTRIBUTING.md at the root. This is ready and provides the complete contribution guidelines so that the subsequent #516 PR can heavily trim AGENTS.md to just link to this file. I updated the PR title as well.

[sadamov]

Thanks a lot for your patience with the review. This past month has been crazy. The approach is good: concise, defers to existing docs rather than duplicating them, and links to authoritative sources.

Required changes

1. Missing CHANGELOG entry

The author checklist item is unchecked and no entry has been added to CHANGELOG.md. Required per project standards. Belongs under ### maintenance in the [unreleased] section, e.g.:

- Add `CONTRIBUTING.md` contributor guide [\#407](https://github.com/mllam/neural-lam/pull/407) @ANANYA542

2. Stale PR description

The description claims the file contains "all 13 pre-commit hooks documented" and "a troubleshooting table" — neither exists in the final file. Please update the PR description to match what was actually committed.

Follow-up items

AGENTS.md deduplication

AGENTS.md contains rules now fully covered by CONTRIBUTING.md:

• PR rule 5: "Run pre-commit hooks locally"
• PR rule 6: "Testing Mandate"
• ### Changelog section

These should be stripped and replaced with a pointer to CONTRIBUTING.md at the top of ## Rules

README.md deduplication

README.md lines 570–578 ("Development and Contributing") now duplicates CONTRIBUTING.md.

[sadamov]

Replace with short URL that is stable:

• Join the [mllam Slack workspace](kutt.to/mllam)