fix: return A0404 for missing PDA pallets

lastleg-service/src/main/java/com/baiyue/lastleg/pda/move/service/PdaInventoryMoveService.java

@@ -51,6 +51,7 @@ public class PdaInventoryMoveService {
         if (existing != null) return replay(existing, requestHash);
 
         var pallet = warehouse.resolvePallet(required(request.sourcePalletCode(), "Source pallet code is required"));
+        if (pallet == null) throw notFound("Source pallet was not found");
         if (pallet.warehouseId() != warehouseId) throw conflict("Source pallet belongs to another overseas warehouse");
         var target = warehouse.resolveLocation(warehouseId,
             required(request.targetLocationCode(), "Target location code is required"));
@@ -188,5 +189,6 @@ public class PdaInventoryMoveService {
     private static long value(Long value) { return value == null ? 0 : value; }
     private static String required(String value, String message) { if (value == null || value.isBlank()) throw badRequest(message); return value.trim(); }
     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 static ResponseStatusException conflict(String message) { return new ResponseStatusException(HttpStatus.CONFLICT, message); }
 }