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/application/src/diary/queries.rs

@@ -0,0 +1,34 @@
+use domain::models::SortDirection;
+use uuid::Uuid;
+
+pub struct GetDiaryQuery {
+    pub limit: Option<u32>,
+    pub offset: Option<u32>,
+    pub sort_by: Option<SortDirection>,
+    pub movie_id: Option<Uuid>,
+    pub user_id: Option<Uuid>,
+}
+
+pub struct GetReviewHistoryQuery {
+    pub movie_id: Uuid,
+}
+
+pub struct GetActivityFeedQuery {
+    pub limit: u32,
+    pub offset: u32,
+    pub sort_by: domain::ports::FeedSortBy,
+    pub search: Option<String>,
+    pub viewer_user_id: Option<Uuid>,
+    pub filter_following: bool,
+}
+
+pub struct ExportQuery {
+    pub user_id: Uuid,
+    pub format: domain::models::ExportFormat,
+}
+
+pub struct GetMovieSocialPageQuery {
+    pub movie_id: uuid::Uuid,
+    pub limit: u32,
+    pub offset: u32,
+}