- Add UserRepository and LinkedAccountRepository protocols to protocols.py
- Add UserEntry and LinkedAccountEntry DTOs for service layer decoupling
- Implement PostgresUserRepository and PostgresLinkedAccountRepository
- Refactor UserService to use constructor-injected repositories
- Add get_user_service factory and UserServiceDep to API deps
- Update auth.py and users.py endpoints to use UserServiceDep
- Rewrite tests to use FastAPI dependency overrides (no monkey patching)
This follows the established repository pattern used by DeckService and
CollectionService, enabling future offline fork support.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
