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/update.rs

@@ -0,0 +1,78 @@
+use uuid::Uuid;
+
+use crate::goals::{
+    commands::{CreateGoalCommand, UpdateGoalCommand},
+    create, update,
+};
+use crate::test_helpers::TestContextBuilder;
+
+#[tokio::test]
+async fn updates_target_count() {
+    let ctx = TestContextBuilder::new().build();
+    create::execute(
+        &ctx,
+        CreateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 10,
+        },
+    )
+    .await
+    .unwrap();
+
+    let result = update::execute(
+        &ctx,
+        UpdateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 100,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert_eq!(result.goal.target_count(), 100);
+}
+
+#[tokio::test]
+async fn fails_when_goal_not_found() {
+    let ctx = TestContextBuilder::new().build();
+    let result = update::execute(
+        &ctx,
+        UpdateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 10,
+        },
+    )
+    .await;
+
+    assert!(result.is_err());
+}
+
+#[tokio::test]
+async fn rejects_zero_target() {
+    let ctx = TestContextBuilder::new().build();
+    create::execute(
+        &ctx,
+        CreateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 10,
+        },
+    )
+    .await
+    .unwrap();
+
+    let result = update::execute(
+        &ctx,
+        UpdateGoalCommand {
+            user_id: Uuid::nil(),
+            year: 2025,
+            target_count: 0,
+        },
+    )
+    .await;
+
+    assert!(result.is_err());
+}