Bump version to 0.3.1

feat(website): update for v0.3.0 with new algorithms

- Update version references from 0.2.0 to 0.3.0
- Add 6 new trainers to trainers page (LightGBM, CatBoost, K-Means, DBSCAN, Isolation Forest, One-Class SVM)
- Organize trainers by category with section headers
- Update stats: 7+ ML Models -> 15+ ML Models
- Update features description to include new algorithms
- Update sidebar with trainer subsections
- Update fallback release data for v0.3.0
- Add v0.3.0 to version selector

Release v0.2.0: Production-ready with docs, examples, and tests

Major improvements:
- Comprehensive documentation structure
- Example configurations for all models
- Test suite with pytest
- Contributing guidelines and code of conduct
- Security policy
- Clean production-ready structure