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>

.env.example

@@ -0,0 +1,24 @@
+APP_ENV=production
+APP_BASE_URL=https://testmyyoutube.vrubel.xyz
+APP_PORT=8080
+APP_SECRET_KEY=CHANGE_ME
+TOKEN_ENCRYPTION_KEY=CHANGE_ME
+
+POSTGRES_PASSWORD=CHANGE_ME
+DATABASE_URL=postgresql+psycopg://youtube_app:CHANGE_ME@postgres:5432/youtube_app
+
+GOOGLE_CLIENT_ID=
+GOOGLE_CLIENT_SECRET=
+GOOGLE_REDIRECT_URI=https://testmyyoutube.vrubel.xyz/api/auth/google/callback
+ALLOWED_GOOGLE_EMAIL=
+
+METUBE_API_BASE_URL=http://192.168.8.177:8081
+METUBE_PUBLIC_BASE_URL=http://192.168.8.177:8081
+METUBE_CONTAINER_DOWNLOAD_DIR=/downloads
+METUBE_REQUEST_TIMEOUT_SECONDS=30
+
+SUBSCRIPTIONS_SYNC_INTERVAL_HOURS=6
+VIDEOS_SYNC_INTERVAL_MINUTES=60
+VIDEOS_PER_CHANNEL_SYNC=10
+
+LOG_LEVEL=INFO