Features:
- Add concurrent embedded mode for multi-process web applications
- Support multiple readers with single-writer coordination
- Lock-free reads with ~100ns latency
- Add Database.open_concurrent() API
- Flask/FastAPI example with Gunicorn workers
- Comprehensive documentation for concurrent mode

License Changes:
- Migrate from Apache-2.0 to AGPL-3.0-or-later
- Update author to full name: Sushanth Reddy Vanagala
- Update PyPI classifier for AGPL license

Technical:
- Add FFI bindings for sochdb_open_concurrent()
- Add is_concurrent property to Database class
- Backward compatible with older library versions
- Performance table comparing standard vs concurrent modes

Testing:
- Import verification passed
- Basic functionality validated
- Ready for web application deployment