refactor: [절곡] import 스크립트 + GuiderailModel code/lot_no 분리 적용

- BendingCleanReimport: code→앞2자리, lot_no→전체코드, 중복체크 lot_no 기준
- BendingImportMissing: 동일 적용
- BendingModelImport: code→접두사(GR/SB/BB), lot_no→전체코드
- MigrateBendingItemsToNewTable: 동일 적용
- GuiderailModelResource: lot_no 필드 추가
- BendingModel: fillable에 lot_no 추가

app/Console/Commands/BendingModelImport.php

@@ -120,7 +120,8 @@ private function importModel(object $row, string $type, string $code, array $dat
         $bm = BendingModel::create(array_merge($data, [
             'tenant_id' => $this->tenantId,
             'model_type' => $type,
-            'code' => $code,
+            'code' => explode('-', $code)[0],
+            'lot_no' => $code,
             'legacy_num' => $row->num,
             'components' => $components,
             'material_summary' => $materialSummary,