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>

backend/app/api/sync.py

@@ -0,0 +1,50 @@
+import logging
+
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy.orm import Session
+
+from app.core.auth_dependency import require_session
+from app.db import get_db
+from app.services import sync
+from app.services.google_oauth import OAuthNotConnected
+from app.services.youtube_client import YouTubeAPIError, YouTubeQuotaExceeded
+
+logger = logging.getLogger(__name__)
+
+router = APIRouter(dependencies=[Depends(require_session)])
+
+
+@router.post("/sync/subscriptions")
+def sync_subscriptions(db: Session = Depends(get_db)) -> dict:
+    try:
+        return sync.sync_subscriptions(db)
+    except sync.SyncInProgress:
+        raise HTTPException(status_code=409, detail="Subscriptions sync already in progress")
+    except OAuthNotConnected:
+        raise HTTPException(status_code=400, detail="Google account is not connected")
+    except YouTubeQuotaExceeded:
+        raise HTTPException(status_code=503, detail="YouTube API quota exhausted")
+    except YouTubeAPIError as exc:
+        raise HTTPException(status_code=502, detail=f"YouTube API error: {exc}")
+
+
+@router.post("/sync/videos")
+def sync_videos(db: Session = Depends(get_db)) -> dict:
+    try:
+        return sync.sync_videos(db)
+    except sync.SyncInProgress:
+        raise HTTPException(status_code=409, detail="Videos sync already in progress")
+    except OAuthNotConnected:
+        raise HTTPException(status_code=400, detail="Google account is not connected")
+    except YouTubeQuotaExceeded:
+        raise HTTPException(status_code=503, detail="YouTube API quota exhausted")
+    except YouTubeAPIError as exc:
+        raise HTTPException(status_code=502, detail=f"YouTube API error: {exc}")
+
+
+@router.get("/sync/status")
+def sync_status(db: Session = Depends(get_db)) -> dict:
+    return {
+        "subscriptions": sync.get_subscriptions_sync_status(db),
+        "videos": sync.get_videos_sync_status(db),
+    }