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/search/execute.rs

@@ -7,3 +7,7 @@ use domain::{
 pub async fn execute(ctx: &AppContext, query: SearchQuery) -> Result<SearchResults, DomainError> {
     ctx.repos.search_port.search(&query).await
 }
+
+#[cfg(test)]
+#[path = "tests/execute.rs"]
+mod tests;

crates/application/src/search/tests/execute.rs

@@ -0,0 +1,16 @@
+use domain::models::SearchQuery;
+
+use crate::search::execute;
+use crate::test_helpers::TestContextBuilder;
+
+#[tokio::test]
+async fn returns_empty_results() {
+    let ctx = TestContextBuilder::new().build();
+
+    let result = execute::execute(&ctx, SearchQuery::default())
+        .await
+        .unwrap();
+
+    assert!(result.movies.items.is_empty());
+    assert!(result.people.items.is_empty());
+}