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/goals/tests/delete.rs

@@ -0,0 +1,59 @@
+use std::sync::Arc;
+
+use domain::testing::{InMemoryGoalRepository, NoopEventPublisher};
+use uuid::Uuid;
+
+use crate::goals::{
+    commands::{CreateGoalCommand, DeleteGoalCommand},
+    create, delete,
+};
+use crate::test_helpers::TestContextBuilder;
+
+#[tokio::test]
+async fn deletes_existing_goal() {
+    let goals = InMemoryGoalRepository::new();
+    let events = NoopEventPublisher::new();
+    let ctx = TestContextBuilder::new()
+        .with_goal(Arc::clone(&goals) as _)
+        .with_event_publisher(Arc::clone(&events) as _)
+        .build();
+
+    create::execute(
+        &ctx,
+        CreateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 10,
+        },
+    )
+    .await
+    .unwrap();
+    assert_eq!(goals.count(), 1);
+
+    delete::execute(
+        &ctx,
+        DeleteGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert_eq!(goals.count(), 0);
+}
+
+#[tokio::test]
+async fn fails_when_not_found() {
+    let ctx = TestContextBuilder::new().build();
+    let result = delete::execute(
+        &ctx,
+        DeleteGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+        },
+    )
+    .await;
+
+    assert!(result.is_err());
+}