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

backend/app/api/admin.py

@@ -130,6 +130,10 @@ async def get_stats(
             WHERE bb.id IS NULL AND bd.raw_text IS NOT NULL
         """)
     )).scalar()
+    # Bills that have never had their action history fetched
+    bills_missing_actions = (await db.execute(
+        text("SELECT COUNT(*) FROM bills WHERE actions_fetched_at IS NULL")
+    )).scalar()
     return {
         "total_bills": total_bills,
         "docs_fetched": docs_fetched,
@@ -141,6 +145,7 @@ async def get_stats(
         "pending_llm": pending_llm,
         "bills_missing_sponsor": bills_missing_sponsor,
         "bills_missing_metadata": bills_missing_metadata,
+        "bills_missing_actions": bills_missing_actions,
         "remaining": total_bills - total_briefs,
     }
 
@@ -183,6 +188,14 @@ async def trigger_fetch_actions(current_user: User = Depends(get_current_admin))
     return {"task_id": task.id, "status": "queued"}
 
 
+@router.post("/backfill-all-actions")
+async def backfill_all_actions(current_user: User = Depends(get_current_admin)):
+    """Queue action fetches for every bill that has never had actions fetched."""
+    from app.workers.congress_poller import backfill_all_bill_actions
+    task = backfill_all_bill_actions.delay()
+    return {"task_id": task.id, "status": "queued"}
+
+
 @router.post("/backfill-metadata")
 async def backfill_metadata(current_user: User = Depends(get_current_admin)):
     """Fill in null introduced_date, congress_url, chamber for existing bills."""