docs: consolidate and clean up documentation

- Remove redundant files: AGENTS.md, INSTRUCTIONS.yaml, instructions.mdc
- Create comprehensive CONTRIBUTING.md with all development guidelines
- Add simple documentation index at docs/README.md
- Update main README to reference consolidated docs
- Remove implementation notes and release summaries
- Keep only essential, current documentation

README.md

@@ -460,8 +460,18 @@ UnitForge uses [uv](https://github.com/astral-sh/uv) for blazing-fast Python pac
 | `make clean` | Clean cache files | Standard |
 | `make status` | Show project status | Standard |
 
-## 📚 systemd Documentation References
+## 📚 Documentation
 
+### 📖 Complete Documentation
+For comprehensive guides and references, see the [**Documentation Index**](docs/README.md):
+
+- **[User Guide](docs/README.md#user-documentation)** - Installation, usage, and configuration
+- **[Developer Guide](CONTRIBUTING.md)** - Development setup and contribution workflow
+- **[Environment Configuration](docs/ENVIRONMENT.md)** - Complete environment variable reference
+- **[Docker Setup](docker/README.md)** - Container development and deployment
+- **[Scripts & Utilities](scripts/README.md)** - Development tools and color utilities
+
+### 🔗 External References
 - [systemd.unit(5)](https://www.freedesktop.org/software/systemd/man/systemd.unit.html) - Unit configuration
 - [systemd.service(5)](https://www.freedesktop.org/software/systemd/man/systemd.service.html) - Service units
 - [systemd.timer(5)](https://www.freedesktop.org/software/systemd/man/systemd.timer.html) - Timer units
@@ -470,25 +480,22 @@ UnitForge uses [uv](https://github.com/astral-sh/uv) for blazing-fast Python pac
 
 ## 🤝 Contributing
 
+**New contributors**: Please see the [**Contributing Guide**](CONTRIBUTING.md) for complete development setup and workflow instructions.
+
+### Quick Contributing Steps
 1. Fork the repository
-2. Create a feature branch: `git checkout -b feature/amazing-feature`
-3. Set up development environment: `make setup-dev`
-4. Make your changes
-5. Add tests for new functionality
-6. Ensure quality checks pass: `make check-all`
-7. Commit your changes: `git commit -m 'Add amazing feature'`
-8. Push to the branch: `git push origin feature/amazing-feature`
-9. Submit a pull request
+2. Set up development environment: `make setup-dev`
+3. Create a feature branch: `git checkout -b feature/amazing-feature`
+4. Make your changes and add tests
+5. Run quality checks: `make dev` (format + lint + test)
+6. Commit and push your changes
+7. Submit a pull request
 
-### Contribution Guidelines
-
-- **Setup**: Use `make setup-dev` for consistent environment (uv required)
-- **Quality**: Run `make check-all` before committing
-- **Tests**: Write tests for new features (`make test-cov`)
-- **Style**: Code is auto-formatted with pre-commit hooks
-- **Type Safety**: Add type hints for Python code
-- **Documentation**: Update docs for API changes
-- **Performance**: Built for uv - no pip fallbacks
+### Key Guidelines
+- **Development Setup**: Use [Contributing Guide](CONTRIBUTING.md) for consistent environment
+- **Quality Assurance**: All code must pass `make dev` (format, lint, test)
+- **Documentation**: Update relevant docs for new features
+- **Testing**: Write tests for new functionality
 
 ## 📄 License