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.rs

@@ -0,0 +1,12 @@
+mod support;
+
+#[path = "auth/login_test.rs"]
+mod login_test;
+#[path = "auth/logout_test.rs"]
+mod logout_test;
+#[path = "auth/refresh_test.rs"]
+mod refresh_test;
+#[path = "auth/register_and_login_test.rs"]
+mod register_and_login_test;
+#[path = "auth/register_test.rs"]
+mod register_test;