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/generate_token.rs

@@ -36,3 +36,7 @@ pub fn hash_token(plaintext: &str) -> String {
     hasher.update(plaintext.as_bytes());
     hex::encode(hasher.finalize())
 }
+
+#[cfg(test)]
+#[path = "tests/generate_token.rs"]
+mod tests;