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/import/commands.rs

@@ -0,0 +1,37 @@
+use domain::models::{FieldMapping, FileFormat};
+use uuid::Uuid;
+
+pub struct CreateImportSessionCommand {
+    pub user_id: Uuid,
+    pub bytes: Vec<u8>,
+    pub format: FileFormat,
+}
+
+pub struct ApplyImportMappingCommand {
+    pub user_id: Uuid,
+    pub session_id: Uuid,
+    pub mappings: Vec<FieldMapping>,
+}
+
+pub struct ExecuteImportCommand {
+    pub user_id: Uuid,
+    pub session_id: Uuid,
+    pub confirmed_indices: Vec<usize>,
+}
+
+pub struct SaveImportProfileCommand {
+    pub user_id: Uuid,
+    pub session_id: Uuid,
+    pub name: String,
+}
+
+pub struct ApplyImportProfileCommand {
+    pub user_id: Uuid,
+    pub session_id: Uuid,
+    pub profile_id: Uuid,
+}
+
+pub struct DeleteImportProfileCommand {
+    pub user_id: Uuid,
+    pub profile_id: Uuid,
+}