refactor: group use cases into DDD bounded contexts

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.

crates/presentation/src/forms.rs

@@ -2,7 +2,7 @@ use chrono::NaiveDateTime;
 use serde::Deserialize;
 use uuid::Uuid;
 
-use application::{
+use application::diary::{
     commands::{LogReviewCommand, MovieInput},
     queries::GetDiaryQuery,
 };