refactor: restructure application to CQRS, update api-types + presentation

- 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

crates/application/Cargo.toml

@@ -11,3 +11,4 @@ thiserror   = { workspace = true }
 uuid        = { workspace = true }
 tokio       = { workspace = true }
 bytes       = { workspace = true }
+serde       = { workspace = true }