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

frontend/components/bills/BriefPanel.tsx

@@ -0,0 +1,116 @@
+"use client";
+
+import { useState } from "react";
+import { ChevronDown, ChevronRight, RefreshCw } from "lucide-react";
+import { BriefSchema } from "@/lib/types";
+import { AIBriefCard } from "@/components/bills/AIBriefCard";
+import { formatDate } from "@/lib/utils";
+
+interface BriefPanelProps {
+  briefs?: BriefSchema[] | null;
+}
+
+const TYPE_LABEL: Record<string, string> = {
+  amendment: "AMENDMENT",
+  full: "FULL",
+};
+
+function typeBadge(briefType?: string) {
+  const label = TYPE_LABEL[briefType ?? ""] ?? (briefType?.toUpperCase() ?? "BRIEF");
+  const isAmendment = briefType === "amendment";
+  return (
+    <span
+      className={`text-xs font-mono px-1.5 py-0.5 rounded ${
+        isAmendment
+          ? "bg-amber-100 text-amber-700 dark:bg-amber-900/40 dark:text-amber-400"
+          : "bg-muted text-muted-foreground"
+      }`}
+    >
+      {label}
+    </span>
+  );
+}
+
+export function BriefPanel({ briefs }: BriefPanelProps) {
+  const [historyOpen, setHistoryOpen] = useState(false);
+  const [expandedId, setExpandedId] = useState<number | null>(null);
+
+  if (!briefs || briefs.length === 0) {
+    return <AIBriefCard brief={null} />;
+  }
+
+  const latest = briefs[0];
+  const history = briefs.slice(1);
+  const isAmendment = latest.brief_type === "amendment";
+
+  return (
+    <div className="space-y-3">
+      {/* "What Changed" badge row */}
+      {isAmendment && (
+        <div className="flex items-center gap-2 px-1">
+          <RefreshCw className="w-3.5 h-3.5 text-amber-500" />
+          <span className="text-sm font-semibold text-amber-600 dark:text-amber-400">
+            What Changed
+          </span>
+          <span className="text-xs text-muted-foreground">·</span>
+          <span className="text-xs text-muted-foreground">{formatDate(latest.created_at)}</span>
+        </div>
+      )}
+
+      {/* Latest brief */}
+      <AIBriefCard brief={latest} />
+
+      {/* Version history (only when there are older briefs) */}
+      {history.length > 0 && (
+        <div className="bg-card border border-border rounded-lg overflow-hidden">
+          <button
+            onClick={() => setHistoryOpen((o) => !o)}
+            className="w-full flex items-center gap-2 px-4 py-3 text-sm font-medium text-muted-foreground hover:text-foreground hover:bg-accent/50 transition-colors text-left"
+          >
+            {historyOpen ? (
+              <ChevronDown className="w-3.5 h-3.5 shrink-0" />
+            ) : (
+              <ChevronRight className="w-3.5 h-3.5 shrink-0" />
+            )}
+            Version History ({history.length} {history.length === 1 ? "version" : "versions"})
+          </button>
+
+          {historyOpen && (
+            <div className="border-t border-border divide-y divide-border">
+              {history.map((brief) => (
+                <div key={brief.id}>
+                  <button
+                    onClick={() =>
+                      setExpandedId((id) => (id === brief.id ? null : brief.id))
+                    }
+                    className="w-full flex items-center gap-3 px-4 py-2.5 text-left hover:bg-accent/40 transition-colors"
+                  >
+                    <span className="text-xs text-muted-foreground w-20 shrink-0">
+                      {formatDate(brief.created_at)}
+                    </span>
+                    {typeBadge(brief.brief_type)}
+                    <span className="text-xs text-muted-foreground truncate flex-1">
+                      {brief.summary?.slice(0, 120) ?? "No summary"}
+                      {(brief.summary?.length ?? 0) > 120 ? "…" : ""}
+                    </span>
+                    {expandedId === brief.id ? (
+                      <ChevronDown className="w-3 h-3 text-muted-foreground shrink-0" />
+                    ) : (
+                      <ChevronRight className="w-3 h-3 text-muted-foreground shrink-0" />
+                    )}
+                  </button>
+
+                  {expandedId === brief.id && (
+                    <div className="px-4 pb-4">
+                      <AIBriefCard brief={brief} />
+                    </div>
+                  )}
+                </div>
+              ))}
+            </div>
+          )}
+        </div>
+      )}
+    </div>
+  );
+}