docs: add CONTRIBUTING.md with pinpoint format, build/test, branch naming, and fork+origin push pattern

CONTRIBUTING.md

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+# Contributing to claw-code
+
+Thanks for your interest. This project follows the **gaebal-gajae pinpoint cadence** — 43+ pinpoints filed and counting. Here's how to contribute effectively.
+
+## Filing a ROADMAP Pinpoint
+
+All feature requests and bug reports go through the pinpoint format (see `ROADMAP.md`). Each pinpoint must have:
+
+- **Exact pinpoint** — one crisp sentence stating what is wrong or missing
+- **Live evidence** — reproduction steps, logs, or observed behavior
+- **Why distinct** — why this isn't already covered by an existing pinpoint
+- **Concrete delta** — what the repo looks like after this is fixed (file-level)
+- **Fix shape** — implementation sketch (function, module, config change)
+
+Vague or duplicate pinpoints will be closed without comment.
+
+## Build & Test
+
+```bash
+# Rust components
+cd rust
+cargo build
+cargo test
+
+# Node / Bun components (if present)
+bun install
+bun test
+```
+
+CI runs on every push. All tests must pass before review.
+
+## Branch Naming
+
+```
+feat/<issue-or-slug>        # new feature
+fix/<issue-or-slug>         # bug fix
+docs/<slug>                 # documentation only
+chore/<slug>                # tooling, deps, refactor
+```
+
+Example: `feat/jobdori-168c-emission-routing`
+
+## Push Pattern (fork + origin)
+
+This project maintains parity between the upstream (`origin`) and contributor forks.
+
+```bash
+# 1. Fork the repo on GitHub, then add your fork as a remote
+git remote add fork https://github.com/<your-username>/claw-code.git
+
+# 2. Create a branch off the target branch
+git checkout -b feat/your-slug origin/feat/target-branch
+
+# 3. Make changes, commit
+git add .
+git commit -m "feat: your change description"
+
+# 4. Push to BOTH remotes (keep parity)
+git push origin feat/your-slug --force-with-lease
+git push fork feat/your-slug --force-with-lease
+
+# 5. Open a PR against the target branch on GitHub
+```
+
+Three-way parity check before opening a PR:
+```bash
+git log --oneline -1 HEAD
+git log --oneline -1 origin/feat/your-slug
+git log --oneline -1 fork/feat/your-slug
+# All three should show the same commit hash
+```
+
+## Code Style
+
+- Rust: `cargo fmt` and `cargo clippy` before committing
+- No dead code, no unused imports
+- Comments in English; commit messages in English
+
+## License
+
+By contributing, you agree your contributions are licensed under the [MIT License](./LICENSE).