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/create_session.rs

@@ -0,0 +1,47 @@
+use chrono::Utc;
+use domain::{
+    errors::DomainError,
+    models::ImportSession,
+    value_objects::{ImportSessionId, UserId},
+};
+
+use crate::{context::AppContext, import::commands::CreateImportSessionCommand};
+
+pub struct CreateSessionResult {
+    pub session_id: ImportSessionId,
+    pub columns: Vec<String>,
+    pub sample_rows: Vec<Vec<String>>,
+}
+
+pub async fn execute(
+    ctx: &AppContext,
+    cmd: CreateImportSessionCommand,
+) -> Result<CreateSessionResult, DomainError> {
+    let user_id = UserId::from_uuid(cmd.user_id);
+    ctx.repos
+        .import_session
+        .delete_expired_for_user(&user_id)
+        .await?;
+
+    let parsed = ctx
+        .services
+        .document_parser
+        .parse(&cmd.bytes, cmd.format)
+        .map_err(|e| DomainError::ValidationError(e.to_string()))?;
+
+    let sample_rows = parsed.rows.iter().take(5).cloned().collect();
+    let columns = parsed.columns.clone();
+
+    let now = Utc::now().naive_utc();
+    let mut session = ImportSession::new(ImportSessionId::generate(), user_id, now);
+    let session_id = session.id.clone();
+    session.parsed_file = Some(parsed);
+
+    ctx.repos.import_session.create(&session).await?;
+
+    Ok(CreateSessionResult {
+        session_id,
+        columns,
+        sample_rows,
+    })
+}