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/movies/discovery_indexer.rs

@@ -0,0 +1,58 @@
+use std::sync::Arc;
+
+use async_trait::async_trait;
+use domain::{
+    errors::DomainError,
+    events::DomainEvent,
+    models::IndexableDocument,
+    ports::{EventHandler, MovieRepository, SearchCommand},
+};
+
+/// Reacts to `MovieDiscovered` and inserts a bare search index entry immediately,
+/// so movies are findable before TMDb enrichment runs.
+/// Enrichment will later overwrite this with the full document (cast, genres, etc.).
+pub struct MovieDiscoveryIndexer {
+    movie_repository: Arc<dyn MovieRepository>,
+    search_command: Arc<dyn SearchCommand>,
+}
+
+impl MovieDiscoveryIndexer {
+    pub fn new(
+        movie_repository: Arc<dyn MovieRepository>,
+        search_command: Arc<dyn SearchCommand>,
+    ) -> Self {
+        Self {
+            movie_repository,
+            search_command,
+        }
+    }
+}
+
+#[async_trait]
+impl EventHandler for MovieDiscoveryIndexer {
+    async fn handle(&self, event: &DomainEvent) -> Result<(), DomainError> {
+        let movie_id = match event {
+            DomainEvent::MovieDiscovered { movie_id, .. } => movie_id.clone(),
+            _ => return Ok(()),
+        };
+
+        let Some(movie) = self.movie_repository.get_movie_by_id(&movie_id).await? else {
+            tracing::warn!(movie_id = %movie_id.value(), "MovieDiscoveryIndexer: movie not found");
+            return Ok(());
+        };
+
+        if let Err(e) = self
+            .search_command
+            .index(IndexableDocument::Movie {
+                id: movie_id.clone(),
+                movie: Box::new(movie),
+                profile: None,
+            })
+            .await
+        {
+            tracing::warn!(movie_id = %movie_id.value(), "failed to index movie on discovery: {e}");
+        }
+
+        Ok(())
+    }
+}