Add CONTRIBUTING, CODE_OF_CONDUCT, issue/PR templates

.github/ISSUE_TEMPLATE.md

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+## What's the issue or request?
+
+## Steps to reproduce (if a bug)
+
+## Expected vs. actual behavior
+
+## Would you like to work on this yourself?

.github/PULL_REQUEST_TEMPLATE.md

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+## What does this change?
+
+## Why?
+
+## Checklist
+- [ ] Gate/eval suite still passes locally
+- [ ] Any threshold change is in config, with a reason in this PR description
+- [ ] No real PII, credentials, or proprietary data added

CODE_OF_CONDUCT.md

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+# Code of Conduct
+
+## Our pledge
+
+We as contributors and maintainers pledge to make participation in this project a harassment-free experience for everyone, regardless of experience level, background, or identity.
+
+## Our standards
+
+Examples of behavior that contributes to a positive environment:
+- Being respectful of differing viewpoints and experiences
+- Giving and gracefully accepting constructive feedback
+- Focusing on what is best for the project and community
+
+Examples of unacceptable behavior:
+- Harassment, insults, or derogatory comments
+- Publishing others' private information without permission
+- Other conduct which could reasonably be considered inappropriate in a professional setting
+
+## Enforcement
+
+Instances of unacceptable behavior may be reported by opening a GitHub issue or contacting the maintainer through their GitHub profile. All complaints will be reviewed and investigated.
+
+This Code of Conduct is adapted from the [Contributor Covenant](https://www.contributor-covenant.org), version 2.1.

CONTRIBUTING.md

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+# Contributing
+
+Thanks for considering a contribution. This repo is part of a small family of "-gate" projects that each enforce one measured bar before letting something ship — please keep contributions in that spirit.
+
+## Ground rules
+
+- **The gate must still pass.** Every PR needs to pass the existing gate/eval suite (CI on this repo). Making the gate stricter or changing what it measures is welcome — but the gate itself has to still run and produce a real pass/fail.
+- **Threshold changes go in config, with a reason.** If you're proposing a change to a pass/fail threshold (a recall bar, a kappa minimum, a spend cap, etc.), change it in the config file where it lives, not by hardcoding a new number inline — and explain *why* in the PR description.
+- **Data stays synthetic.** All fixtures, golden sets, and example data in this repo are synthetic or public-domain. Don't add real PII, real credentials, real account data, or anything proprietary.
+
+## Getting started
+
+1. Fork the repo and clone your fork.
+2. Follow the Quickstart in the README to get a working local environment (no API key required for the base path).
+3. Run the test suite and the gate locally before opening a PR — both should be green (or, for a deliberately-failing example, fail for the expected reason).
+4. Open a PR against `main`. Small, focused PRs are easier to review than large ones.
+
+## Good first issues
+
+Issues labeled `good first issue` are scoped to be approachable without deep context on the rest of the repo. `help wanted` issues are open to anyone.
+
+## Code of conduct
+
+This project follows the [Code of Conduct](CODE_OF_CONDUCT.md).