Refactor customer form and service for company ID validation.

internal/customer/handler.go

@@ -133,6 +133,9 @@ func (h *Handler) UpdateCustomer(c echo.Context) error {
 			err.Error() == "company with this tax ID already exists" {
 			return response.Conflict(c, err.Error())
 		}
+		if strings.HasPrefix(err.Error(), "invalid company ID") {
+			return response.BadRequest(c, err.Error(), err.Error())
+		}
 		return response.InternalServerError(c, "Failed to update customer")
 	}