Add comprehensive architecture documentation

Document all major SDK components including:
- Database connectivity (MySQL and HTTP connectors)
- Connection abstraction with DB-API 2.0 interface
- SingleStore-specific features (vectors, extended types, result formats)
- Configuration system
- Management API for cloud workspaces
- Fusion SQL client-side extensions
- External functions (UDFs) with execution modes
- AI integration and vector store
- Notebook integration with live accessor objects
- Testing infrastructure with Docker container management

Include ASCII diagrams for connection flow, cursor hierarchy,
management API, Fusion SQL dispatch, and UDF execution modes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kesmit13