Refactor: ATProto Repository Storage with Indigo Carstore Integration

- Remove blob storage from repository interface and implementation
- Add GORM integration for better database management
- Integrate Indigo's carstore for proper CAR file storage
- Update repository wrapper to use external blockstore
- Add comprehensive test infrastructure with test database setup
- Add test environment configuration example
- Update dependencies to include required Indigo and IPFS packages
- Fix repository record operations to work without inline value storage
- Add proper error handling and migrations for carstore integration

This refactoring aligns the repository storage with ATProto standards by:
1. Using Indigo's carstore for efficient CAR file management
2. Removing custom blob storage in favor of standard IPFS blockstore
3. Improving test infrastructure for better integration testing

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Feature/lexicon implementation

Implements full-stack user functionality following layered architecture:
- User domain models and validation
- RESTful API endpoints (GET /users/{id}, POST /users)
- PostgreSQL database with migrations and indexes
- Repository pattern with interfaces
- Service layer with business logic
- Integration tests and error handling
- Docker Compose for local development

🤖 Generated with Claude Code

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