feat: add feed sidebar and cursor-based pagination

Add a feed sidebar to /unread and /read pages for filtering articles by
feed, and replace the fixed 100-article limit with cursor-based
pagination using a "Load more" button.

Backend:
- Add PageInfo, ArticleConnection types and pagination args to GraphQL
- Replace GetUnreadArticles/GetReadArticles with parameterized queries
- Add GetFeedUnreadCounts query and composite index
- Add shared pagination helper in resolver

Frontend:
- Add FeedSidebar component with unread count badges
- Add usePaginatedArticles hook for cursor-based fetching
- Update ArticleList with Load more button and single-feed mode
- Use ?feed=<id> query parameter for feed filtering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/backend/db/queries/feeds.sql b/backend/db/queries/feeds.sql
index acf36d2..094a0f8 100644
--- a/backend/db/queries/feeds.sql
+++ b/backend/db/queries/feeds.sql
@@ -37,3 +37,10 @@ WHERE is_subscribed = 1;
 UPDATE feeds
 SET is_subscribed = 0
 WHERE id = ?;
+
+-- name: GetFeedUnreadCounts :many
+SELECT f.id as feed_id, COUNT(a.id) as unread_count
+FROM feeds AS f
+LEFT JOIN articles AS a ON f.id = a.feed_id AND a.is_read = 0
+WHERE f.is_subscribed = 1 AND f.user_id = ?
+GROUP BY f.id;