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/integrations/tests/generate_token.rs

@@ -0,0 +1,39 @@
+use std::sync::Arc;
+
+use domain::models::WatchEventSource;
+use domain::testing::InMemoryWebhookTokenRepository;
+use uuid::Uuid;
+
+use crate::integrations::{commands::GenerateWebhookTokenCommand, generate_token};
+use crate::test_helpers::TestContextBuilder;
+
+#[tokio::test]
+async fn generates_token_and_saves() {
+    let tokens = InMemoryWebhookTokenRepository::new();
+    let ctx = TestContextBuilder::new()
+        .with_webhook_tokens(Arc::clone(&tokens) as _)
+        .build();
+
+    let user_id = Uuid::new_v4();
+    let result = generate_token::execute(
+        &ctx,
+        GenerateWebhookTokenCommand {
+            user_id,
+            provider: WatchEventSource::Jellyfin,
+            label: None,
+        },
+    )
+    .await
+    .unwrap();
+
+    assert!(!result.token_plaintext.is_empty());
+
+    let saved = ctx
+        .repos
+        .webhook_token
+        .list_by_user(&domain::value_objects::UserId::from_uuid(user_id))
+        .await
+        .unwrap();
+    assert_eq!(saved.len(), 1);
+    assert_eq!(saved[0].id().value(), result.token.id().value());
+}