fix: proactively fetch votes for stanced bills + register vote_fetcher with Celery

vote_fetcher was missing from Celery's include list (task not registered with
workers) and had no beat schedule — votes only fetched on-demand when a user
visited a bill's votes page. Stanced bills (pocket_veto/pocket_boost) never had
votes fetched, leaving the alignment page blank.

Add fetch_votes_for_stanced_bills nightly task (4:30 AM UTC) that queues
fetch_bill_votes for every bill any user has stanced but has no stored votes.
Register vote_fetcher in the include list and add it to the polling queue route.

Authored by: Jack Levy

backend/app/workers/vote_fetcher.py

@@ -237,3 +237,35 @@ def fetch_bill_votes(self, bill_id: str) -> dict:
         return {"bill_id": bill_id, "stored": stored, "skipped": skipped}
     finally:
         db.close()
+
+
+@celery_app.task(bind=True, name="app.workers.vote_fetcher.fetch_votes_for_stanced_bills")
+def fetch_votes_for_stanced_bills(self) -> dict:
+    """
+    Nightly task: queue vote fetches for every bill any user has a stance on
+    (pocket_veto or pocket_boost). Only queues bills that don't already have
+    a vote stored, so re-runs are cheap after the first pass.
+    """
+    from app.models.follow import Follow
+
+    db = get_sync_db()
+    try:
+        from sqlalchemy import text as sa_text
+        rows = db.execute(sa_text("""
+            SELECT DISTINCT f.follow_value AS bill_id
+            FROM follows f
+            LEFT JOIN bill_votes bv ON bv.bill_id = f.follow_value
+            WHERE f.follow_type = 'bill'
+              AND f.follow_mode IN ('pocket_veto', 'pocket_boost')
+              AND bv.id IS NULL
+        """)).fetchall()
+
+        queued = 0
+        for row in rows:
+            fetch_bill_votes.delay(row.bill_id)
+            queued += 1
+
+        logger.info(f"fetch_votes_for_stanced_bills: queued {queued} bills")
+        return {"queued": queued}
+    finally:
+        db.close()