docs: add CONTRIBUTING.md

[Gingiris]

Why

The repo has no CONTRIBUTING.md. External contributors currently have to reverse-engineer expectations from merged PRs, REVIEW.md, and the README. A contributing guide lowers that friction — particularly useful now that the project is gaining attention and receiving more external PRs.

What this adds

• Development setup — install steps using uv, env file configuration
• Branch and commit conventions — inferred from existing branch names in the repo (fix/, feat/, docs/, ci/)
• Code style — type annotations, docstring expectations, async handler pattern consistent with agent/core/tools.py
• Testing — how to run pytest, what to test, where tests live
• PR type guidelines — bug fixes, docs, new tools, config changes, CI changes
• Review standards summary — P0/P1/P2 levels from REVIEW.md, what to expect from the automated Claude review
• FAQ — draft PRs, lock file changes, getting started

What this does not do

• Does not change any code.
• Does not introduce new processes — everything here is already implied by the codebase and REVIEW.md.
• Does not make claims about merge timelines or guarantees.

Verification

• All internal links (README.md, REVIEW.md) point to files that exist at the repo root.
• Checked branch naming conventions against actual branches in the repo.
• ToolSpec pattern description matches agent/core/tools.py.

[fglogan]

closed per maintainer request

[Gingiris]

Understood — thanks for the note, @fglogan. No worries at all. If the maintainers ever want to revisit a contributing guide down the line, happy to help. Good luck with the project!

[Gingiris]

Closing this per earlier feedback. Apologies for the delay in cleaning up. Thank you! 🙏