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/ports.rs

@@ -1,7 +1,16 @@
+use async_trait::async_trait;
 use uuid::Uuid;
 
+use domain::errors::DomainError;
 use domain::models::DiaryEntry;
 
+use crate::diary::commands::LogReviewCommand;
+
+#[async_trait]
+pub trait ReviewLogger: Send + Sync {
+    async fn log_review(&self, cmd: LogReviewCommand) -> Result<(), DomainError>;
+}
+
 pub struct HtmlPageContext {
     pub user_email: Option<String>,
     pub user_id: Option<Uuid>,