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/App.tsx

@@ -0,0 +1,55 @@
+import { useQuery } from '@tanstack/react-query'
+import { Route, Routes } from 'react-router-dom'
+import { getAuthStatus } from './api/client'
+import Connect from './pages/Connect'
+import Feed from './pages/Feed'
+import Channels from './pages/Channels'
+import ChannelVideos from './pages/ChannelVideos'
+import VideoPage from './pages/VideoPage'
+import Categories from './pages/Categories'
+import './App.css'
+
+function App() {
+  const { data, isLoading, isError } = useQuery({
+    queryKey: ['auth-status'],
+    queryFn: getAuthStatus,
+  })
+
+  if (isLoading) {
+    return (
+      <div className="app">
+        <p>Загрузка...</p>
+      </div>
+    )
+  }
+
+  if (isError) {
+    return (
+      <div className="app">
+        <p className="error">Backend недоступен</p>
+      </div>
+    )
+  }
+
+  if (!data?.authenticated) {
+    return (
+      <div className="app">
+        <Connect />
+      </div>
+    )
+  }
+
+  return (
+    <div className="app">
+      <Routes>
+        <Route path="/" element={<Feed />} />
+        <Route path="/channels" element={<Channels />} />
+        <Route path="/channels/:channelId/videos" element={<ChannelVideos />} />
+        <Route path="/video/:youtubeVideoId" element={<VideoPage />} />
+        <Route path="/categories" element={<Categories />} />
+      </Routes>
+    </div>
+  )
+}
+
+export default App