fix(scripts): SQLAlchemy 트랜잭션 에러 수정

autobegin 상태에서 begin() 재호출 에러 → engine.begin() 컨텍스트 매니저로 변경.
189건 PostgreSQL weight_min_kg/weight_max_kg 업데이트 완료.

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

backend/scripts/fill_weight_from_dosage.py

@@ -524,23 +524,20 @@ def main():
     # ── DB 업데이트 ──
     if not dry_run and updates:
         print(f'\n  DB 업데이트 시작...')
-        tx = conn.begin()
-        try:
+        conn.close()
+        with pg.begin() as tx_conn:
             for apc_code, wmin, wmax, _, _ in updates:
-                conn.execute(text('''
+                tx_conn.execute(text('''
                     UPDATE apc
                     SET weight_min_kg = :wmin, weight_max_kg = :wmax
                     WHERE apc = :apc
                 '''), {'wmin': wmin, 'wmax': wmax, 'apc': apc_code})
-            tx.commit()
-            print(f'  완료: {len(updates)}건 업데이트')
-        except Exception as e:
-            tx.rollback()
-            print(f'  오류 발생, 롤백: {e}')
+        print(f'  완료: {len(updates)}건 업데이트')
     elif not dry_run and not updates:
         print('\n  업데이트할 항목이 없습니다.')
-
-    conn.close()
+        conn.close()
+    else:
+        conn.close()
     print('\n완료.')