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/presentation/src/state.rs

@@ -1,26 +1,26 @@
 use std::sync::Arc;
-use application::use_cases::{GetProfile, LoginUser, RegisterUser};
+use application::identity::{RegisterUserHandler, LoginUserHandler, GetProfileHandler};
 
 use domain::ports::{StoragePort, TokenIssuer};
 
 
 #[derive(Clone)]
 pub struct AppState {
-    pub register_uc: Arc<RegisterUser>,
-    pub login_uc: Arc<LoginUser>,
-    pub get_profile_uc: Arc<GetProfile>,
+    pub register_handler: Arc<RegisterUserHandler>,
+    pub login_handler: Arc<LoginUserHandler>,
+    pub get_profile_handler: Arc<GetProfileHandler>,
     pub token_issuer: Arc<dyn TokenIssuer>,
     pub storage: Arc<dyn StoragePort>,
 }
 
 impl AppState {
     pub fn new(
-        register_uc: Arc<RegisterUser>,
-        login_uc: Arc<LoginUser>,
-        get_profile_uc: Arc<GetProfile>,
+        register_handler: Arc<RegisterUserHandler>,
+        login_handler: Arc<LoginUserHandler>,
+        get_profile_handler: Arc<GetProfileHandler>,
         token_issuer: Arc<dyn TokenIssuer>,
         storage: Arc<dyn StoragePort>,
     ) -> Self {
-        Self { register_uc, login_uc, get_profile_uc, token_issuer, storage }
+        Self { register_handler, login_handler, get_profile_handler, token_issuer, storage }
     }
 }