Add identity authentication flow and database migration support

[rgomids]

Summary

• add identity domain, application, persistence, and HTTP layers for account creation, password login, session invalidation, and authenticated principal resolution
• add PostgreSQL migration execution and bootstrap persistence updates, including core identity schema setup
• update user module integration points, error handling, configuration, and operational documentation
• add coverage across unit, integration, and functional tests for identity, persistence, config, and health flows

Testing

• Not run (not requested)