fix(members): link sponsors to bills and fix member search

- Poller now fetches bill detail on insert to get sponsor (list endpoint
  has no sponsor data)
- Add backfill_sponsor_ids task + admin endpoint + UI button to fix the
  1,616 existing bills with NULL sponsor_id
- Member name search now matches both "Last, First" and "First Last"
  using split_part() on the stored name column; same fix applied to
  global search
- Load Bill.sponsor relationship eagerly in get_member_bills to prevent
  MissingGreenlet error during Pydantic serialization
- Remove .trim() on search onChange so spaces can be typed

Authored-By: Jack Levy

backend/app/api/admin.py

@@ -110,6 +110,13 @@ async def get_stats(
 
 # ── Celery Tasks ──────────────────────────────────────────────────────────────
 
+@router.post("/backfill-sponsors")
+async def backfill_sponsors(current_user: User = Depends(get_current_admin)):
+    from app.workers.congress_poller import backfill_sponsor_ids
+    task = backfill_sponsor_ids.delay()
+    return {"task_id": task.id, "status": "queued"}
+
+
 @router.post("/trigger-poll")
 async def trigger_poll(current_user: User = Depends(get_current_admin)):
     from app.workers.congress_poller import poll_congress_bills