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/goals.rs

@@ -0,0 +1,12 @@
+mod support;
+
+#[path = "goals/create_test.rs"]
+mod create_test;
+#[path = "goals/delete_test.rs"]
+mod delete_test;
+#[path = "goals/get_test.rs"]
+mod get_test;
+#[path = "goals/list_test.rs"]
+mod list_test;
+#[path = "goals/update_test.rs"]
+mod update_test;