add 400+ unit tests for domain and application layers

Extract ReviewLogger trait to decouple import/integrations
from diary::log_review (cross-module coupling smell).

Add in-memory fakes for all repository ports, enabling
isolated testing of every use case module without a database.

Coverage: domain+application 22% → 80%, 427 tests.

crates/application/src/integrations/get_queue.rs

@@ -9,3 +9,7 @@ pub async fn execute(
     let user_id = UserId::from_uuid(query.user_id);
     ctx.repos.watch_event.list_pending(&user_id).await
 }
+
+#[cfg(test)]
+#[path = "tests/get_queue.rs"]
+mod tests;