feat: bill action pipeline, What Changed UI, citation backfill, admin panel

Backend:
- Add fetch_bill_actions task with pagination and idempotent upsert
- Add fetch_actions_for_active_bills nightly batch (4 AM UTC beat schedule)
- Wire fetch_bill_actions into new-bill creation and _update_bill_if_changed
- Add backfill_brief_citations task: detects pre-citation briefs by JSONB
  type check, deletes them, re-queues LLM processing against stored text
  (LLM calls only — zero Congress.gov or GovInfo calls)
- Add admin endpoints: POST /bills/{id}/reprocess, /backfill-citations,
  /trigger-fetch-actions; add uncited_briefs count to /stats

Frontend:
- New BriefPanel component: wraps AIBriefCard, adds amber "What Changed"
  badge for amendment briefs and collapsible version history with
  inline brief expansion
- Swap AIBriefCard for BriefPanel on bill detail page
- Admin panel: Backfill Citations + Fetch Bill Actions buttons; amber
  warning in stats when uncited briefs remain
- Add feature roadmap document with phased plan through Phase 5

Co-Authored-By: Jack Levy

backend/app/api/admin.py

@@ -1,5 +1,5 @@
 from fastapi import APIRouter, Depends, HTTPException
-from sqlalchemy import func, select
+from sqlalchemy import func, select, text
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.dependencies import get_current_admin
@@ -98,18 +98,35 @@ async def get_stats(
     amendment_briefs = (await db.execute(
         select(func.count()).select_from(BillBrief).where(BillBrief.brief_type == "amendment")
     )).scalar()
+    uncited_briefs = (await db.execute(
+        text("""
+            SELECT COUNT(*) FROM bill_briefs
+            WHERE key_points IS NOT NULL
+              AND jsonb_array_length(key_points) > 0
+              AND jsonb_typeof(key_points->0) = 'string'
+        """)
+    )).scalar()
     return {
         "total_bills": total_bills,
         "docs_fetched": docs_fetched,
         "briefs_generated": total_briefs,
         "full_briefs": full_briefs,
         "amendment_briefs": amendment_briefs,
+        "uncited_briefs": uncited_briefs,
         "remaining": total_bills - total_briefs,
     }
 
 
 # ── Celery Tasks ──────────────────────────────────────────────────────────────
 
+@router.post("/backfill-citations")
+async def backfill_citations(current_user: User = Depends(get_current_admin)):
+    """Delete pre-citation briefs and re-queue LLM processing using stored document text."""
+    from app.workers.llm_processor import backfill_brief_citations
+    task = backfill_brief_citations.delay()
+    return {"task_id": task.id, "status": "queued"}
+
+
 @router.post("/backfill-sponsors")
 async def backfill_sponsors(current_user: User = Depends(get_current_admin)):
     from app.workers.congress_poller import backfill_sponsor_ids
@@ -131,6 +148,13 @@ async def trigger_member_sync(current_user: User = Depends(get_current_admin)):
     return {"task_id": task.id, "status": "queued"}
 
 
+@router.post("/trigger-fetch-actions")
+async def trigger_fetch_actions(current_user: User = Depends(get_current_admin)):
+    from app.workers.congress_poller import fetch_actions_for_active_bills
+    task = fetch_actions_for_active_bills.delay()
+    return {"task_id": task.id, "status": "queued"}
+
+
 @router.post("/trigger-trend-scores")
 async def trigger_trend_scores(current_user: User = Depends(get_current_admin)):
     from app.workers.trend_scorer import calculate_all_trend_scores
@@ -138,6 +162,16 @@ async def trigger_trend_scores(current_user: User = Depends(get_current_admin)):
     return {"task_id": task.id, "status": "queued"}
 
 
+@router.post("/bills/{bill_id}/reprocess")
+async def reprocess_bill(bill_id: str, current_user: User = Depends(get_current_admin)):
+    """Queue document and action fetches for a specific bill. Useful for debugging."""
+    from app.workers.document_fetcher import fetch_bill_documents
+    from app.workers.congress_poller import fetch_bill_actions
+    doc_task = fetch_bill_documents.delay(bill_id)
+    actions_task = fetch_bill_actions.delay(bill_id)
+    return {"task_ids": {"documents": doc_task.id, "actions": actions_task.id}}
+
+
 @router.get("/task-status/{task_id}")
 async def get_task_status(task_id: str, current_user: User = Depends(get_current_admin)):
     from app.workers.celery_app import celery_app