feat: per-user notifications (ntfy + RSS), deduplicated actions, backfill task

Notifications:
- New /notifications page accessible to all users (ntfy + RSS config)
- ntfy now supports no-auth, Bearer token, and HTTP Basic auth (for ACL-protected self-hosted servers)
- RSS enabled/disabled independently of ntfy; token auto-generated on first GET
- Notification settings removed from admin-only Settings page; replaced with link card
- Sidebar adds Notifications nav link for all users
- notification_dispatcher.py: fan-out now marks RSS events dispatched independently

Action history:
- Migration 0012: deduplicates existing bill_actions rows and adds UNIQUE(bill_id, action_date, action_text)
- congress_poller.py: replaces existence-check inserts with ON CONFLICT DO NOTHING (race-condition safe)
- Added backfill_all_bill_actions task (no date filter) + admin endpoint POST /backfill-all-actions

Authored-By: Jack Levy

frontend/lib/api.ts

@@ -161,6 +161,7 @@ export interface AnalysisStats {
   pending_llm: number;
   bills_missing_sponsor: number;
   bills_missing_metadata: number;
+  bills_missing_actions: number;
   remaining: number;
 }
 
@@ -199,6 +200,8 @@ export const adminAPI = {
     apiClient.post("/api/admin/backfill-citations").then((r) => r.data),
   triggerFetchActions: () =>
     apiClient.post("/api/admin/trigger-fetch-actions").then((r) => r.data),
+  backfillAllActions: () =>
+    apiClient.post("/api/admin/backfill-all-actions").then((r) => r.data),
   backfillMetadata: () =>
     apiClient.post("/api/admin/backfill-metadata").then((r) => r.data),
   resumeAnalysis: () =>