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/users/get_settings_test.rs

@@ -0,0 +1,18 @@
+use crate::support::TestContextBuilder;
+use uuid::Uuid;
+
+use application::users::{deps::GetSettingsDeps, get_settings};
+
+#[tokio::test]
+async fn returns_default_settings() {
+    let b = TestContextBuilder::new();
+    let deps = GetSettingsDeps {
+        user_settings: b.user_settings_repo.clone(),
+    };
+
+    let settings = get_settings::execute(&deps, Uuid::nil()).await.unwrap();
+
+    assert!(settings.federate_goals());
+    assert!(settings.federate_reviews());
+    assert!(settings.federate_watchlist());
+}