v1.9.1: docs: update README for v1.9.0 and bump version to 1.9.1
- Updated README with v1.9.0 features and improvements - Consolidated version history and breaking changes section - Bumped version to 1.9.1 for documentation release 🤖 Generated with [Claude Code](https://claude.ai/code) Co-Authored-By: Claude <noreply@anthropic.com>