Add comprehensive CLAUDE.md documentation for AI assistants

Created detailed guide covering:
- Project overview and architecture
- Complete repository structure explanation
- Technology stack and dependencies
- Database models and relationships
- Configuration hierarchy and options
- Development workflow and setup
- Code conventions and patterns
- Testing practices
- API structure and versioning
- Common development tasks and workflows
- Security considerations
- Deployment guidelines
- CI/CD pipeline information
- Quick reference commands

This guide provides AI assistants with comprehensive context about
the ExaFS codebase structure, development practices, and key conventions
to follow when working with the project.

Author: claude