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

frontend/lib/api.ts

@@ -151,6 +151,8 @@ export const adminAPI = {
     apiClient.post("/api/admin/trigger-member-sync").then((r) => r.data),
   triggerTrendScores: () =>
     apiClient.post("/api/admin/trigger-trend-scores").then((r) => r.data),
+  backfillSponsors: () =>
+    apiClient.post("/api/admin/backfill-sponsors").then((r) => r.data),
   getTaskStatus: (taskId: string) =>
     apiClient.get(`/api/admin/task-status/${taskId}`).then((r) => r.data),
 };