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_activity_feed.rs

@@ -0,0 +1,71 @@
+use crate::{context::AppContext, diary::queries::GetActivityFeedQuery};
+use domain::{
+    errors::DomainError,
+    models::{
+        FeedEntry,
+        collections::{PageParams, Paginated},
+    },
+    ports::FollowingFilter,
+};
+
+pub async fn execute(
+    ctx: &AppContext,
+    query: GetActivityFeedQuery,
+) -> Result<Paginated<FeedEntry>, DomainError> {
+    let page = PageParams::new(Some(query.limit), Some(query.offset))?;
+
+    let following = build_following_filter(ctx, &query).await;
+
+    ctx.repos
+        .diary
+        .query_activity_feed_filtered(
+            &page,
+            &query.sort_by,
+            query.search.as_deref(),
+            following.as_ref(),
+        )
+        .await
+}
+
+async fn build_following_filter(
+    _ctx: &AppContext,
+    query: &GetActivityFeedQuery,
+) -> Option<FollowingFilter> {
+    #[cfg(not(feature = "federation"))]
+    {
+        let _ = query;
+        return None;
+    }
+    #[cfg(feature = "federation")]
+    {
+        if !query.filter_following {
+            return None;
+        }
+        let viewer_id = match query.viewer_user_id {
+            Some(id) => id,
+            None => return None,
+        };
+        let urls = _ctx
+            .repos
+            .social_query
+            .get_accepted_following_urls(viewer_id)
+            .await
+            .unwrap_or_default();
+        let base_url = &_ctx.config.base_url;
+        let mut local_ids = vec![viewer_id];
+        let mut remote_urls = Vec::new();
+        for url in urls {
+            if let Some(suffix) = url.strip_prefix(&format!("{}/users/", base_url))
+                && let Ok(parsed_id) = uuid::Uuid::parse_str(suffix)
+            {
+                local_ids.push(parsed_id);
+                continue;
+            }
+            remote_urls.push(url);
+        }
+        Some(FollowingFilter {
+            local_user_ids: local_ids,
+            remote_actor_urls: remote_urls,
+        })
+    }
+}