fix: full force_rebuild 시 universe_snapshot 전체 삭제

tickers=None (전체 빌드)일 때 registry에서 제거된 stale 티커 데이터도
정리되도록 DELETE FROM universe_snapshot 실행.

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

app/services/universe_service.py

@@ -290,7 +290,12 @@ class UniverseService:
             )
 
             if force_rebuild:
-                # Delete in chunks to avoid huge IN clauses
+                if not tickers:
+                    # Full rebuild: wipe ALL snapshots (also removes stale tickers
+                    # that were de-registered from the registry)
+                    await db.execute(UniverseSnapshot.__table__.delete())
+                else:
+                    # Partial rebuild: delete only the requested tickers
                     for i in range(0, len(ticker_list), _CHUNK):
                         chunk = ticker_list[i:i + _CHUNK]
                         await db.execute(