docs: add CLAUDE.md for Claude Code

CLAUDE.md

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+# config-commitlint
+
+> Shared commitlint configuration for Flagbit projects. Published to npm as `@flagbit/config-commitlint`, it extends `@commitlint/config-conventional` with stricter rules (sentence-case body/subject, mandatory references, 72-char line limits, enforced type enum).
+
+## Tech Stack
+- Node.js, plain CommonJS (`index.js`)
+- `@commitlint/cli` ^12, `@commitlint/config-conventional` ^12
+
+## Repository Structure
+- `index.js` — the exported commitlint rule set (the package's main entry)
+- `commitlint.config.js` — local config used to lint this repo's own commits (extends `index.js`, adds Jira issue-prefix parser)
+- `Makefile` — single `lint` target for CI and local use
+
+## Build / Test / Lint
+
+```bash
+# Install dependencies
+npm ci           # or: yarn
+
+# Lint commits since origin/master (default)
+make lint
+
+# Lint commits since a specific base
+GITHUB_BASE_REF=main make lint
+```
+
+`make lint` runs `commitlint` against all commits from `origin/$GITHUB_BASE_REF` to `HEAD`.
+
+## Conventions
+- Conventional Commits enforced by this package's own rules
+- Releases are automated via `release-please` on push to `master`; merging a release PR triggers `npm publish --access public`
+- Do **not** write commits with `chore: release` as the subject — they are intentionally ignored by commitlint
+- References footer is **required** in every commit (e.g. `References: IS-123`)
+
+## Gotchas / Notes
+- Local install: if your `.npmrc` routes `@flagbit` to a private registry, install with `--registry https://registry.npmjs.org` to pull from npm
+- `header-min-length: 30` — subjects shorter than 30 characters will fail linting