docs: add contribution guidelines

Author: giginet

AGENTS.md

@@ -0,0 +1,33 @@
+# Vibe Coding Guidelines
+
+This repository uses Node.js and TypeScript. Please follow these rules when
+contributing:
+
+## Setup
+
+- Use Node.js version listed in `.node-version`.
+- Install dependencies with `npm ci`.
+
+## Formatting
+
+- All files are formatted with Prettier.
+- Run `npm run format:write` before committing. CI will check
+  `npm run format:check`.
+
+## Linting
+
+- Lint source code with ESLint using `npm run lint`.
+
+## Testing
+
+- Run `npm test` (or `npm run ci-test`) to execute Jest tests.
+- Add tests for new functionality under `__test__/`.
+
+## Packaging
+
+- Build distributable files with `npm run package`.
+
+## Pull Requests
+
+- Keep commits concise and use the imperative mood.
+- Ensure tests and linting pass before opening a PR.