- application: replace flat use_cases/ with identity/{commands,queries}/ and organization/commands/
- each use case now split into Command/Query struct + Handler struct
- api-types: add username to RegisterRequest/UserResponse, add CreateAlbumRequest/AlbumResponse
- presentation: update state, handlers, factory to use new handler types
- tests: restructured to match CQRS module layout, added get_profile tests
