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/src/organization/commands/create_album.rs

@@ -0,0 +1,32 @@
+use std::sync::Arc;
+use domain::{
+    entities::Album,
+    errors::DomainError,
+    ports::AlbumRepository,
+    value_objects::SystemId,
+};
+
+#[derive(Debug, Clone, serde::Serialize, serde::Deserialize)]
+pub struct CreateAlbumCommand {
+    pub title: String,
+    pub creator_id: SystemId,
+}
+
+pub struct CreateAlbumHandler {
+    album_repo: Arc<dyn AlbumRepository>,
+}
+
+impl CreateAlbumHandler {
+    pub fn new(album_repo: Arc<dyn AlbumRepository>) -> Self {
+        Self { album_repo }
+    }
+
+    pub async fn execute(&self, cmd: CreateAlbumCommand) -> Result<Album, DomainError> {
+        if cmd.title.is_empty() {
+            return Err(DomainError::Validation("Album title must not be empty".to_string()));
+        }
+        let album = Album::new(&cmd.title, cmd.creator_id);
+        self.album_repo.save(&album).await?;
+        Ok(album)
+    }
+}

crates/application/src/organization/commands/mod.rs

@@ -0,0 +1,3 @@
+pub mod create_album;
+
+pub use create_album::{CreateAlbumCommand, CreateAlbumHandler};

crates/application/src/organization/mod.rs

@@ -0,0 +1,3 @@
+pub mod commands;
+
+pub use commands::{CreateAlbumCommand, CreateAlbumHandler};