fix: return A0404 for missing PDA pallets

lastleg-service/src/main/java/com/baiyue/lastleg/palletops/service/PdaPalletOperationService.java

@@ -367,6 +367,7 @@ public class PdaPalletOperationService {
 
     private PalletPhysicalGateway.PalletReference requirePallet(long warehouseId, String code) {
         PalletPhysicalGateway.PalletReference pallet = physical.resolve(code(code));
+        if (pallet == null) throw notFound("未找到托盘");
         if (pallet.warehouseId() != warehouseId) throw conflict("托盘不属于 Token 冻结的海外仓");
         if ("SCRAPPED".equals(pallet.status())) throw conflict("已报废托盘不能执行作业");
         return pallet;
@@ -517,6 +518,7 @@ public class PdaPalletOperationService {
     private static long value(Long value) { return value == null ? 0L : value; }
     private static ResponseStatusException conflict(String message) { return new ResponseStatusException(HttpStatus.CONFLICT, message); }
     private static ResponseStatusException badRequest(String message) { return new ResponseStatusException(HttpStatus.BAD_REQUEST, message); }
+    private static ResponseStatusException notFound(String message) { return new ResponseStatusException(HttpStatus.NOT_FOUND, message); }
 
     private record PlannedMove(long positionId, long packages, long expectedVersion,
                                long sourcePalletId, String sourcePalletCode,