refactor: group use cases into DDD bounded contexts

Flat use_cases/ (44 files) + monolithic commands.rs/queries.rs
split into diary/, movies/, watchlist/, import/, auth/, users/,
integrations/, search/, person/, federation/ — each with own
commands.rs, queries.rs, and use case modules.

Inline tests extracted to sibling tests/ dirs.

crates/application/src/diary/tests/log_review.rs

@@ -0,0 +1,111 @@
+use std::sync::Arc;
+
+use chrono::Utc;
+
+use domain::{
+    models::Movie,
+    value_objects::{MovieTitle, ReleaseYear},
+};
+
+use domain::ports::MovieRepository;
+use domain::testing::{InMemoryMovieRepository, InMemoryReviewRepository, NoopEventPublisher};
+
+use crate::{
+    diary::commands::{LogReviewCommand, MovieInput},
+    diary::log_review,
+    test_helpers::TestContextBuilder,
+};
+
+fn movie_input_manual(title: &str, year: u16) -> MovieInput {
+    MovieInput {
+        movie_id: None,
+        external_metadata_id: None,
+        manual_title: Some(title.to_string()),
+        manual_release_year: Some(year),
+        manual_director: None,
+    }
+}
+
+fn movie_input_by_id(id: uuid::Uuid) -> MovieInput {
+    MovieInput {
+        movie_id: Some(id),
+        external_metadata_id: None,
+        manual_title: None,
+        manual_release_year: None,
+        manual_director: None,
+    }
+}
+
+#[tokio::test]
+async fn test_log_review_creates_movie_and_review() {
+    let movies = InMemoryMovieRepository::new();
+    let reviews = InMemoryReviewRepository::new();
+    let events = NoopEventPublisher::new();
+    let ctx = TestContextBuilder::new()
+        .with_movies(Arc::clone(&movies) as _)
+        .with_reviews(Arc::clone(&reviews) as _)
+        .with_event_publisher(Arc::clone(&events) as _)
+        .build();
+
+    let user_id = uuid::Uuid::new_v4();
+    let cmd = LogReviewCommand {
+        user_id,
+        input: movie_input_manual("Blade Runner", 1982),
+        rating: 4,
+        comment: None,
+        watched_at: Utc::now().naive_utc(),
+    };
+
+    log_review::execute(&ctx, cmd).await.unwrap();
+
+    assert_eq!(reviews.count(), 1, "review should be saved");
+    assert!(!events.published().is_empty(), "events should be published");
+}
+
+#[tokio::test]
+async fn test_log_review_reuses_existing_movie() {
+    let movies = InMemoryMovieRepository::new();
+    let reviews = InMemoryReviewRepository::new();
+
+    let existing_movie = Movie::new(
+        None,
+        MovieTitle::new("Alien".into()).unwrap(),
+        ReleaseYear::new(1979).unwrap(),
+        None,
+        None,
+    );
+    let movie_uuid = existing_movie.id().value();
+    movies.upsert_movie(&existing_movie).await.unwrap();
+
+    let ctx = TestContextBuilder::new()
+        .with_movies(Arc::clone(&movies) as _)
+        .with_reviews(Arc::clone(&reviews) as _)
+        .build();
+
+    let cmd = LogReviewCommand {
+        user_id: uuid::Uuid::new_v4(),
+        input: movie_input_by_id(movie_uuid),
+        rating: 5,
+        comment: None,
+        watched_at: Utc::now().naive_utc(),
+    };
+
+    log_review::execute(&ctx, cmd).await.unwrap();
+
+    assert_eq!(movies.count(), 1, "no duplicate movie");
+    assert_eq!(reviews.count(), 1);
+}
+
+#[tokio::test]
+async fn test_log_review_with_invalid_rating_fails() {
+    let ctx = TestContextBuilder::new().build();
+    let cmd = LogReviewCommand {
+        user_id: uuid::Uuid::new_v4(),
+        input: movie_input_manual("Some Film", 2000),
+        rating: 6,
+        comment: None,
+        watched_at: Utc::now().naive_utc(),
+    };
+    let result = log_review::execute(&ctx, cmd).await;
+    assert!(result.is_err(), "rating > 5 should fail");
+}