feat: M2 (part 2) — RSS poller, backfill, enrichment, scheduler

- Free per-channel RSS reader for quota-less fresh-video detection
- Recent-first backfill (configurable: 100 videos / 1 year) plus resumable deep
  backfill from the uploads playlist
- Enrichment via videos.list: duration, view/like counts, category, topics,
  language, Shorts heuristic and livestream/premiere classification
- Reusable sync runners + APScheduler jobs (rss / enrich / backfill), all
  quota-aware with a reserve so backfill never starves fresh enrichment
- Manual triggers: POST /api/sync/{rss,backfill,enrich}
- Exact insert counting via RETURNING with in-batch de-duplication

backend/app/routes/sync.py

@@ -6,11 +6,24 @@ from app import quota
 from app.auth import current_user
 from app.db import get_db
 from app.models import Channel, Subscription, User, Video
+from app.sync.runner import run_enrich, run_recent_backfill, run_rss_poll
 from app.sync.subscriptions import import_subscriptions
 
 router = APIRouter(prefix="/api/sync", tags=["sync"])
 
 
+def _user_channels(db: Session, user: User) -> list[Channel]:
+    return (
+        db.execute(
+            select(Channel)
+            .join(Subscription, Subscription.channel_id == Channel.id)
+            .where(Subscription.user_id == user.id)
+        )
+        .scalars()
+        .all()
+    )
+
+
 @router.post("/subscriptions")
 def sync_subscriptions(
     user: User = Depends(current_user), db: Session = Depends(get_db)
@@ -22,6 +35,38 @@ def sync_subscriptions(
     return result
 
 
+@router.post("/rss")
+def sync_rss(
+    user: User = Depends(current_user), db: Session = Depends(get_db)
+) -> dict:
+    new = run_rss_poll(db, _user_channels(db, user))
+    return {"new_videos": new}
+
+
+@router.post("/backfill")
+def sync_backfill(
+    user: User = Depends(current_user),
+    db: Session = Depends(get_db),
+    max_channels: int = 25,
+) -> dict:
+    before = quota.units_used_today(db)
+    result = run_recent_backfill(db, _user_channels(db, user), max_channels=max_channels)
+    result["quota_used_estimate"] = quota.units_used_today(db) - before
+    return result
+
+
+@router.post("/enrich")
+def sync_enrich(
+    user: User = Depends(current_user), db: Session = Depends(get_db)
+) -> dict:
+    before = quota.units_used_today(db)
+    enriched = run_enrich(db)
+    return {
+        "enriched": enriched,
+        "quota_used_estimate": quota.units_used_today(db) - before,
+    }
+
+
 @router.get("/status")
 def sync_status(
     user: User = Depends(current_user), db: Session = Depends(get_db)