feat: Member Effectiveness Score + Representation Alignment View (v0.9.9)

Member Effectiveness Score
- New BillCosponsor table (migration 0018) with per-bill co-sponsor
  party data required for the bipartisan multiplier
- bill_category column on Bill (substantive | commemorative | administrative)
  set by a cheap one-shot LLM call after each brief is generated
- effectiveness_score / percentile / tier columns on Member
- New bill_classifier.py worker with 5 tasks:
    classify_bill_category  — triggered from llm_processor after brief
    fetch_bill_cosponsors   — triggered from congress_poller on new bill
    calculate_effectiveness_scores — nightly at 5 AM UTC
    backfill_bill_categories / backfill_all_bill_cosponsors — one-time
- Scoring: distance-traveled pts × bipartisan (1.5×) × substance (0.1×
  for commemorative) × leadership (1.2× for committee chairs)
- Percentile normalised within (seniority tier × party) buckets
- Effectiveness card on member detail page with colour-coded bar
- Admin panel: 3 new backfill/calculate controls in Maintenance section

Representation Alignment View
- New GET /api/alignment endpoint: cross-references user's stanced bill
  follows (pocket_veto/pocket_boost) with followed members' vote positions
- Efficient bulk queries — no N+1 loops
- New /alignment page with ranked member list and alignment bars
- Alignment added to sidebar nav (auth-required)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/workers/celery_app.py

@@ -17,6 +17,7 @@ celery_app = Celery(
         "app.workers.member_interest",
         "app.workers.notification_dispatcher",
         "app.workers.llm_batch_processor",
+        "app.workers.bill_classifier",
     ],
 )
 
@@ -37,6 +38,7 @@ celery_app.conf.update(
         "app.workers.document_fetcher.*": {"queue": "documents"},
         "app.workers.llm_processor.*": {"queue": "llm"},
         "app.workers.llm_batch_processor.*": {"queue": "llm"},
+        "app.workers.bill_classifier.*": {"queue": "llm"},
         "app.workers.news_fetcher.*": {"queue": "news"},
         "app.workers.trend_scorer.*": {"queue": "news"},
         "app.workers.member_interest.*": {"queue": "news"},
@@ -96,5 +98,9 @@ celery_app.conf.update(
             "task": "app.workers.llm_batch_processor.poll_llm_batch_results",
             "schedule": crontab(minute="*/30"),
         },
+        "calculate-effectiveness-scores": {
+            "task": "app.workers.bill_classifier.calculate_effectiveness_scores",
+            "schedule": crontab(hour=5, minute=0),  # 5 AM UTC, after all other nightly tasks
+        },
     },
 )