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/celery_app.py

@@ -18,6 +18,7 @@ celery_app = Celery(
         "app.workers.notification_dispatcher",
         "app.workers.llm_batch_processor",
         "app.workers.bill_classifier",
+        "app.workers.vote_fetcher",
     ],
 )
 
@@ -43,6 +44,7 @@ celery_app.conf.update(
         "app.workers.trend_scorer.*": {"queue": "news"},
         "app.workers.member_interest.*": {"queue": "news"},
         "app.workers.notification_dispatcher.*": {"queue": "polling"},
+        "app.workers.vote_fetcher.*": {"queue": "polling"},
     },
     task_queues=[
         Queue("polling"),
@@ -82,6 +84,10 @@ celery_app.conf.update(
             "task": "app.workers.congress_poller.fetch_actions_for_active_bills",
             "schedule": crontab(hour=4, minute=0),  # 4 AM UTC, after trend + member scoring
         },
+        "fetch-votes-for-stanced-bills": {
+            "task": "app.workers.vote_fetcher.fetch_votes_for_stanced_bills",
+            "schedule": crontab(hour=4, minute=30),  # 4:30 AM UTC daily
+        },
         "dispatch-notifications": {
             "task": "app.workers.notification_dispatcher.dispatch_notifications",
             "schedule": crontab(minute="*/5"),  # Every 5 minutes