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/workers/congress_poller.py

@@ -10,6 +10,7 @@ import time
 from datetime import datetime, timedelta, timezone
 
 from sqlalchemy import or_
+from sqlalchemy.dialects.postgresql import insert as pg_insert
 
 from app.database import get_sync_db
 from app.models import Bill, BillAction, Member, AppSetting
@@ -227,30 +228,15 @@ def fetch_bill_actions(self, bill_id: str):
                 break
 
             for action in actions_data:
-                action_date_str = action.get("actionDate")
-                action_text = action.get("text", "")
-                action_type = action.get("type")
-                chamber = action.get("chamber")
-
-                # Idempotency check: skip if (bill_id, action_date, action_text) exists
-                exists = (
-                    db.query(BillAction)
-                    .filter(
-                        BillAction.bill_id == bill_id,
-                        BillAction.action_date == action_date_str,
-                        BillAction.action_text == action_text,
-                    )
-                    .first()
-                )
-                if not exists:
-                    db.add(BillAction(
-                        bill_id=bill_id,
-                        action_date=action_date_str,
-                        action_text=action_text,
-                        action_type=action_type,
-                        chamber=chamber,
-                    ))
-                    inserted += 1
+                stmt = pg_insert(BillAction.__table__).values(
+                    bill_id=bill_id,
+                    action_date=action.get("actionDate"),
+                    action_text=action.get("text", ""),
+                    action_type=action.get("type"),
+                    chamber=action.get("chamber"),
+                ).on_conflict_do_nothing(constraint="uq_bill_actions_bill_date_text")
+                result = db.execute(stmt)
+                inserted += result.rowcount
 
             db.commit()
             offset += 250
@@ -297,6 +283,28 @@ def fetch_actions_for_active_bills(self):
         db.close()
 
 
+@celery_app.task(bind=True, name="app.workers.congress_poller.backfill_all_bill_actions")
+def backfill_all_bill_actions(self):
+    """One-time backfill: enqueue action fetches for every bill that has never had actions fetched."""
+    db = get_sync_db()
+    try:
+        bills = (
+            db.query(Bill)
+            .filter(Bill.actions_fetched_at.is_(None))
+            .order_by(Bill.latest_action_date.desc())
+            .all()
+        )
+        queued = 0
+        for bill in bills:
+            fetch_bill_actions.delay(bill.bill_id)
+            queued += 1
+            time.sleep(0.05)  # ~20 tasks/sec — workers will self-throttle against Congress.gov
+        logger.info(f"backfill_all_bill_actions: queued {queued} bills")
+        return {"queued": queued}
+    finally:
+        db.close()
+
+
 def _update_bill_if_changed(db, existing: Bill, parsed: dict) -> bool:
     """Update bill fields if anything has changed. Returns True if updated."""
     changed = False