fix(reconcile): symbol을 슬롯 생성 시 함께 저장 + NULL 슬롯 backfill

reconcile_universe 시그니처를 set[str] → dict[str, str] (portfolio_id→symbol)로 변경.
기존 symbol=NULL 슬롯은 다음 reconcile 실행 시 자동 backfill.

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

tests/adapters/messaging/test_rabbitmq_intent_e2e.py

@@ -54,7 +54,7 @@ def test_intent_admission_rpc_dedups_duplicate_correlation_id_over_rabbitmq(mq_u
     svc = SlotService(repo)
     intents = IntentService(svc, repo, InMemoryIntentStore(),
                             resolve_symbol=lambda pid: "005930")  # dcy-011: universe resolve
-    repo.reconcile_universe("default", {"PF-1"})
+    repo.reconcile_universe("default", {"PF-1": "SYM"})
     handler = make_intent_rpc_handler(intents)
 
     queue = f"trex.test.intent.{uuid.uuid4().hex[:8]}"