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/diary/tests/get_diary.rs

@@ -0,0 +1,22 @@
+use crate::{diary::get_diary, diary::queries::GetDiaryQuery, test_helpers::TestContextBuilder};
+
+#[tokio::test]
+async fn returns_empty_page() {
+    let ctx = TestContextBuilder::new().build();
+
+    let result = get_diary::execute(
+        &ctx,
+        GetDiaryQuery {
+            limit: None,
+            offset: None,
+            sort_by: None,
+            movie_id: None,
+            user_id: None,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(result.items.is_empty());
+    assert_eq!(result.total_count, 0);
+}