refactor: group use cases into DDD bounded contexts

Flat use_cases/ (44 files) + monolithic commands.rs/queries.rs
split into diary/, movies/, watchlist/, import/, auth/, users/,
integrations/, search/, person/, federation/ — each with own
commands.rs, queries.rs, and use case modules.

Inline tests extracted to sibling tests/ dirs.

crates/application/src/users/get_users.rs

@@ -0,0 +1,28 @@
+use crate::{context::AppContext, users::queries::GetUsersQuery};
+use domain::{errors::DomainError, models::UserSummary, ports::RemoteActorInfo};
+
+pub struct UsersListData {
+    pub users: Vec<UserSummary>,
+    pub remote_actors: Vec<RemoteActorInfo>,
+}
+
+pub async fn execute(
+    ctx: &AppContext,
+    _query: GetUsersQuery,
+) -> Result<UsersListData, DomainError> {
+    #[cfg(feature = "federation")]
+    let (users_result, actors_result) = tokio::join!(
+        ctx.repos.user.list_with_stats(),
+        ctx.repos.social_query.list_all_followed_remote_actors()
+    );
+    #[cfg(not(feature = "federation"))]
+    let (users_result, actors_result) = (
+        ctx.repos.user.list_with_stats().await,
+        Ok::<Vec<RemoteActorInfo>, DomainError>(vec![]),
+    );
+
+    Ok(UsersListData {
+        users: users_result?,
+        remote_actors: actors_result?,
+    })
+}