docs: update README to V4 API with comprehensive documentation and AI assistant guidance

- Updated API version references from v2 to V4 throughout documentation
- Added AI assistant guidance section at top explaining automatic login and optional configuration
- Restructured documentation with clear sections: Quickstart, Constructor, Options, CRUD methods, Special methods
- Simplified examples and removed redundant explanations
- Consolidated session caching documentation with clearer examples for

Author: pitw