test: move application tests to tests/

test_support/test_helpers -> tests/support; watched_at unified w/ domain test_watched_at (2024-03-15).
Kept inline: users::diary_filter tests (feed_sort_to_direction_all_variants, paged_user_filter_builds_correctly) - pub(super) helpers in private module.
Dropped stale never-compiled users/tests/get_users.rs (old execute signature).

crates/application/tests/auth/register_and_login_test.rs

@@ -0,0 +1,30 @@
+use crate::support::TestContextBuilder;
+use application::auth::commands::RegisterAndLoginCommand;
+use application::auth::deps::RegisterAndLoginDeps;
+use application::auth::register_and_login;
+
+#[tokio::test]
+async fn registers_and_returns_token() {
+    let b = TestContextBuilder::new();
+    let deps = RegisterAndLoginDeps {
+        user: b.user_repo.clone(),
+        password_hasher: b.password_hasher.clone(),
+        auth: b.auth_service.clone(),
+        refresh_session: b.refresh_session_repo.clone(),
+        config: b.config.clone(),
+    };
+
+    let result = register_and_login::execute(
+        &deps,
+        RegisterAndLoginCommand {
+            email: "new@example.com".into(),
+            username: "newuser".into(),
+            password: "password123".into(),
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(!result.token.is_empty());
+    assert_eq!(result.email, "new@example.com");
+}