chore: comprehensive cleanup and documentation improvements

Simplifies tooling configuration and enhances documentation for better
developer experience and visual clarity.

Changes:
- Consolidated linting to Biome only, removed ESLint dependencies
- Removed eslint.config.mjs and updated package.json scripts
- Rewrote CONTRIBUTING.md with clear workflow and visual structure
- Rewrote README.md optimized for visual learners with better hierarchy
- Applied Biome auto-fixes (flatMap, numeric separators, Node.js imports)
- All 191 tests passing with maintained coverage

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jdalton

CONTRIBUTING.md

@@ -1,18 +1,83 @@
-# Contributing
+# Contributing to packageurl-js
 
-Contributions are welcome and appreciated!
-Every little bit helps, and credit will always be given.
+Thanks for your interest in contributing! Every contribution helps make this project better.
 
-When contributing to purl (such as code, bugs, documentation, etc.) you
-agree to the Developer Certificate of Origin http://developercertificate.org/
-and its license (see the mit.LICENSE file).  The same approach is used
-by the Linux Kernel developers and several other projects.
+## Quick Start
 
-For commits, it is best to simply add a line like this to your commit message,
-with your name and email:
+```bash
+# 1. Fork and clone the repository
+git clone https://github.com/<your-username>/packageurl-js.git
+cd packageurl-js
+
+# 2. Install dependencies (requires pnpm)
+pnpm install
+
+# 3. Make your changes and run tests
+pnpm test
+
+# 4. Lint and format your code
+pnpm run fix
 ```
-    Signed-off-by: Jane Doe <developer@example.com>
+
+## Development Workflow
+
+### Before You Submit
+
+- ✅ Run `pnpm test` - all tests must pass
+- ✅ Run `pnpm run fix` - auto-format code
+- ✅ Run `pnpm run check:tsc` - type-check passes
+- ✅ Add tests for new features
+- ✅ Update docs if needed
+
+### Commit Messages
+
+Write clear, descriptive commit messages:
+
+```bash
+# Good examples
+git commit -m "fix: handle percent encoding in qualifiers"
+git commit -m "feat: add support for pub package type"
+git commit -m "docs: clarify namespace requirements"
+
+# Include sign-off
+Signed-off-by: Your Name <your.email@example.com>
 ```
 
-Please try to write a good commit message.
-See: https://chris.beams.io/posts/git-commit/
+See [How to Write a Git Commit Message](https://chris.beams.io/posts/git-commit/) for more tips.
+
+### Developer Certificate of Origin
+
+By contributing, you agree to the [Developer Certificate of Origin](http://developercertificate.org/) and the [MIT License](LICENSE).
+
+## Testing
+
+### Run Tests
+
+```bash
+pnpm test              # Run all tests
+pnpm run check:tsc     # Type checking
+```
+
+### Test Structure
+
+- `test/package-url.spec.js` - Main test suite (includes purl-spec compliance tests)
+- `test/benchmark.spec.js` - Performance benchmarks
+- `test/data/` - Test fixtures
+
+## Code Style
+
+This project uses [Biome](https://biomejs.dev/) for formatting and linting:
+
+- **Format**: 2 spaces, 80 char line width
+- **Style**: Single quotes, trailing commas
+- **Auto-fix**: `pnpm run fix`
+
+## Need Help?
+
+- 💬 [Open an issue](https://github.com/package-url/packageurl-js/issues) for questions
+- 🐛 Report bugs with a minimal reproduction
+- 💡 Suggest features with use cases
+
+## License
+
+[MIT](LICENSE) © the purl authors