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.
Flat use_cases/ (44 files) + monolithic commands.rs/queries.rs
split into diary/, movies/, watchlist/, import/, auth/, users/,
integrations/, search/, person/, federation/ — each with own
commands.rs, queries.rs, and use case modules.
Inline tests extracted to sibling tests/ dirs.
