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/get_movie_social_page.rs

@@ -0,0 +1,45 @@
+use domain::{
+    errors::DomainError,
+    models::{
+        FeedEntry, Movie, MovieProfile, MovieStats,
+        collections::{PageParams, Paginated},
+    },
+    value_objects::MovieId,
+};
+
+use crate::{context::AppContext, diary::queries::GetMovieSocialPageQuery};
+
+pub struct MovieSocialPageResult {
+    pub movie: Movie,
+    pub stats: MovieStats,
+    pub reviews: Paginated<FeedEntry>,
+    pub profile: Option<MovieProfile>,
+}
+
+pub async fn execute(
+    ctx: &AppContext,
+    query: GetMovieSocialPageQuery,
+) -> Result<MovieSocialPageResult, DomainError> {
+    let movie_id = MovieId::from_uuid(query.movie_id);
+    let page = PageParams::new(Some(query.limit), Some(query.offset))?;
+
+    let movie = ctx
+        .repos
+        .movie
+        .get_movie_by_id(&movie_id)
+        .await?
+        .ok_or_else(|| DomainError::NotFound(format!("Movie {}", query.movie_id)))?;
+
+    let (stats, reviews, profile) = tokio::try_join!(
+        ctx.repos.diary.get_movie_stats(&movie_id),
+        ctx.repos.diary.get_movie_social_feed(&movie_id, &page),
+        ctx.repos.movie_profile.get_by_movie_id(&movie_id),
+    )?;
+
+    Ok(MovieSocialPageResult {
+        movie,
+        stats,
+        reviews,
+        profile,
+    })
+}