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/movies/tests/sync_poster.rs

@@ -0,0 +1,103 @@
+use std::sync::Arc;
+
+use uuid::Uuid;
+
+use domain::{
+    errors::DomainError,
+    models::Movie,
+    ports::{MetadataClient, MovieRepository},
+    testing::InMemoryMovieRepository,
+    value_objects::{ExternalMetadataId, MovieTitle, PosterUrl, ReleaseYear},
+};
+
+use crate::{
+    diary::commands::SyncPosterCommand, movies::sync_poster, test_helpers::TestContextBuilder,
+};
+
+#[tokio::test]
+async fn fails_when_movie_not_found() {
+    let ctx = TestContextBuilder::new().build();
+
+    let result = sync_poster::execute(
+        &ctx,
+        SyncPosterCommand {
+            movie_id: Uuid::new_v4(),
+        },
+    )
+    .await;
+
+    assert!(result.is_err());
+}
+
+#[tokio::test]
+async fn fails_when_no_external_id() {
+    let movies = InMemoryMovieRepository::new();
+    let movie = Movie::new(
+        None,
+        MovieTitle::new("Test".into()).unwrap(),
+        ReleaseYear::new(2024).unwrap(),
+        None,
+        None,
+    );
+    let movie_id = movie.id().value();
+    movies.upsert_movie(&movie).await.unwrap();
+
+    let ctx = TestContextBuilder::new()
+        .with_movies(Arc::clone(&movies) as _)
+        .build();
+
+    let result = sync_poster::execute(&ctx, SyncPosterCommand { movie_id }).await;
+
+    assert!(result.is_err());
+}
+
+struct FakeMetaWithPoster;
+
+#[async_trait::async_trait]
+impl MetadataClient for FakeMetaWithPoster {
+    async fn fetch_movie_metadata(
+        &self,
+        _: &domain::ports::MetadataSearchCriteria,
+    ) -> Result<Movie, DomainError> {
+        unimplemented!()
+    }
+    async fn get_poster_url(
+        &self,
+        _: &ExternalMetadataId,
+    ) -> Result<Option<PosterUrl>, DomainError> {
+        Ok(Some(
+            PosterUrl::new("https://example.com/poster.jpg".into()).unwrap(),
+        ))
+    }
+}
+
+#[tokio::test]
+async fn syncs_poster_for_movie_with_external_id() {
+    let movies = InMemoryMovieRepository::new();
+    let ext_id = ExternalMetadataId::new("tmdb:999".into()).unwrap();
+    let movie = Movie::new(
+        Some(ext_id),
+        MovieTitle::new("Poster Movie".into()).unwrap(),
+        ReleaseYear::new(2024).unwrap(),
+        None,
+        None,
+    );
+    let movie_id = movie.id().value();
+    movies.upsert_movie(&movie).await.unwrap();
+
+    let ctx = TestContextBuilder::new()
+        .with_movies(Arc::clone(&movies) as _)
+        .with_metadata_client(Arc::new(FakeMetaWithPoster) as _)
+        .build();
+
+    sync_poster::execute(&ctx, SyncPosterCommand { movie_id })
+        .await
+        .unwrap();
+
+    let updated = movies
+        .get_movie_by_id(&domain::value_objects::MovieId::from_uuid(movie_id))
+        .await
+        .unwrap()
+        .unwrap();
+    assert!(updated.poster_path().is_some());
+}