Implement Phases 1-5: skeleton, OAuth, categories, video sync/feed, playback

- FastAPI + PostgreSQL + Alembic + React/Vite skeleton, Docker Compose, healthcheck
- Google OAuth (single allowed account), encrypted refresh token storage
- Subscriptions sync with pagination, uploads playlist batch fetch
- Categories CRUD, many-to-many channel assignment, category filtering
- Video sync (playlistItems + videos.list batching), cached feed with cursor
  pagination, background scheduler (APScheduler)
- Video detail page with YouTube embed player
- SPA fallback routing, optimistic UI updates, client-side query caching

40 backend tests covering OAuth allow-list, sync idempotency, cascade deletes,
cursor pagination, and category filtering.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/ChannelVideos.tsx

@@ -0,0 +1,56 @@
+import { useInfiniteQuery, useQuery } from '@tanstack/react-query'
+import { Link, useParams } from 'react-router-dom'
+import { getChannel, getFeed } from '../api/client'
+import VideoCard from '../components/VideoCard'
+
+function ChannelVideos() {
+  const { channelId } = useParams<{ channelId: string }>()
+  const id = Number(channelId)
+
+  const channelQuery = useQuery({ queryKey: ['channel', id], queryFn: () => getChannel(id) })
+
+  const feedQuery = useInfiniteQuery({
+    queryKey: ['feed', 'channel', id],
+    queryFn: ({ pageParam }) => getFeed({ channelId: id, cursor: pageParam }),
+    initialPageParam: undefined as string | undefined,
+    getNextPageParam: (lastPage) => lastPage.next_cursor ?? undefined,
+  })
+
+  const items = feedQuery.data?.pages.flatMap((page) => page.items) ?? []
+
+  return (
+    <div className="feed-screen">
+      <header>
+        <div>
+          <Link to="/channels" className="back-link">
+            ← Каналы
+          </Link>
+          <h1>{channelQuery.data?.title ?? 'Канал'}</h1>
+        </div>
+      </header>
+
+      {feedQuery.isLoading && <p>Загрузка...</p>}
+      {feedQuery.isError && <p className="error">Не удалось загрузить видео</p>}
+
+      <ul className="video-grid">
+        {items.map((video) => (
+          <VideoCard key={video.youtube_video_id} video={video} />
+        ))}
+      </ul>
+
+      {!feedQuery.isLoading && items.length === 0 && <p>У этого канала пока нет синхронизированных видео.</p>}
+
+      {feedQuery.hasNextPage && (
+        <button
+          className="load-more"
+          onClick={() => feedQuery.fetchNextPage()}
+          disabled={feedQuery.isFetchingNextPage}
+        >
+          {feedQuery.isFetchingNextPage ? 'Загрузка...' : 'Показать ещё'}
+        </button>
+      )}
+    </div>
+  )
+}
+
+export default ChannelVideos