feat: domain mocks, TestContextBuilder, use case tests, factory pattern

- Add test-helpers feature to domain crate with in-memory mocks and panic stubs for all ports
- Add TestContextBuilder to application crate for zero-database test setup
- Add unit tests for log_review, register, login, add_to_watchlist, delete_review use cases
- Extract DatabaseAdapters factory and build_* helpers into presentation/src/factory.rs
- Refactor wire_dependencies() in main.rs to use factory module

crates/application/src/lib.rs

@@ -10,5 +10,8 @@ pub mod search_cleanup;
 pub mod use_cases;
 pub mod worker;
 
+#[cfg(test)]
+pub mod test_helpers;
+
 pub use movie_discovery_indexer::MovieDiscoveryIndexer;
 pub use search_cleanup::SearchCleanupHandler;