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/Feed.tsx

@@ -0,0 +1,102 @@
+import { useMutation, useInfiniteQuery, useQuery, useQueryClient } from '@tanstack/react-query'
+import { Link } from 'react-router-dom'
+import { getFeed, getSyncStatus, listCategories, logout, syncVideos } from '../api/client'
+import CategoryNav, { type CategoryFilter } from '../components/CategoryNav'
+import VideoCard from '../components/VideoCard'
+import { useState } from 'react'
+
+function Feed() {
+  const [filter, setFilter] = useState<CategoryFilter>('all')
+  const queryClient = useQueryClient()
+
+  const categoriesQuery = useQuery({ queryKey: ['categories'], queryFn: listCategories })
+  const categories = categoriesQuery.data ?? []
+
+  const feedQuery = useInfiniteQuery({
+    queryKey: ['feed', filter],
+    queryFn: ({ pageParam }) =>
+      getFeed({
+        categoryId: typeof filter === 'number' ? filter : undefined,
+        uncategorized: filter === 'uncategorized',
+        cursor: pageParam,
+      }),
+    initialPageParam: undefined as string | undefined,
+    getNextPageParam: (lastPage) => lastPage.next_cursor ?? undefined,
+  })
+
+  const syncStatusQuery = useQuery({
+    queryKey: ['sync-status'],
+    queryFn: getSyncStatus,
+    refetchInterval: (query) => (query.state.data?.videos.running ? 1500 : false),
+  })
+
+  const syncMutation = useMutation({
+    mutationFn: syncVideos,
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['feed'] })
+      queryClient.invalidateQueries({ queryKey: ['sync-status'] })
+    },
+  })
+
+  const logoutMutation = useMutation({
+    mutationFn: logout,
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['auth-status'] })
+    },
+  })
+
+  const running = syncStatusQuery.data?.videos.running
+  const items = feedQuery.data?.pages.flatMap((page) => page.items) ?? []
+
+  return (
+    <div className="feed-screen">
+      <header>
+        <h1>Лента</h1>
+        <div className="actions">
+          <Link to="/channels">Каналы</Link>
+          <Link to="/categories">Категории</Link>
+          <button onClick={() => syncMutation.mutate()} disabled={running}>
+            {running ? 'Синхронизация...' : 'Обновить сейчас'}
+          </button>
+          <button onClick={() => logoutMutation.mutate()}>Выйти</button>
+        </div>
+      </header>
+
+      {syncMutation.isError && <p className="error">{(syncMutation.error as Error).message}</p>}
+      {syncStatusQuery.data?.videos.status === 'failed' && (
+        <p className="error">Последняя синхронизация видео завершилась ошибкой: {syncStatusQuery.data.videos.error}</p>
+      )}
+
+      <div className="layout">
+        <CategoryNav categories={categories} value={filter} onChange={setFilter} />
+
+        <div className="content">
+          {feedQuery.isLoading && <p>Загрузка...</p>}
+          {feedQuery.isError && <p className="error">Не удалось загрузить ленту</p>}
+
+          <ul className="video-grid">
+            {items.map((video) => (
+              <VideoCard key={video.youtube_video_id} video={video} />
+            ))}
+          </ul>
+
+          {!feedQuery.isLoading && items.length === 0 && (
+            <p>Видео пока нет. Нажми "Обновить сейчас" или проверь, есть ли каналы в этой категории.</p>
+          )}
+
+          {feedQuery.hasNextPage && (
+            <button
+              className="load-more"
+              onClick={() => feedQuery.fetchNextPage()}
+              disabled={feedQuery.isFetchingNextPage}
+            >
+              {feedQuery.isFetchingNextPage ? 'Загрузка...' : 'Показать ещё'}
+            </button>
+          )}
+        </div>
+      </div>
+    </div>
+  )
+}
+
+export default Feed