Failed to Move VM to Another Account

### problem

Up on stopping an Instance and trying to move it to another account...

...it does not make clear what caused the failure.

Even as a Root Admin, there is no explanation of what prevented the move from happening.

By looking at the logs, the message is clear but it is followed by an unhandled exception.

Sanitized fragments of the logs:

```
2026-06-11 20:07:53,953 ERROR [o.a.c.a.c.a.v.AssignVMCmd] (qtp1404565079-58786:[ctx-e08ee8a2, ctx-7b35ebda]) (logid:46523a5c) Failed to move VM [4944]. com.cloud.exception.InvalidParameterValueException: Snapshots exist for volume [ROOT-4944]. Detach volume or remove snapshots for the volume before assigning VM to another user.
at com.cloud.vm.UserVmManagerImpl.validateIfVolumesHaveNoSnapshots(UserVmManagerImpl.java:7961)
at com.cloud.vm.UserVmManagerImpl.moveVmToUser(UserVmManagerImpl.java:7871)
```

```
2026-06-11 19:58:58,841 ERROR [o.a.c.a.c.a.v.AssignVMCmd] (qtp1404565079-58786:[ctx-b7b9a764, ctx-86b9f79a]) (logid:1096b7f6) Failed to move VM [4944]. com.cloud.exception.InvalidParameterValueException: Remove any Port Forwarding rules for VM [VM instance {"id":4944,"instanceName":"i-73-4944-VM","state":"Stopped","type":"User","uuid":"*"}] before assigning it to another user.
at com.cloud.vm.UserVmManagerImpl.validateIfVmHasNoRules(UserVmManagerImpl.java:7934)
at com.cloud.vm.UserVmManagerImpl.moveVmToUser(UserVmManagerImpl.java:7868)
```

### versions

ACS 4.22.0.1

### The steps to reproduce the bug

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### What to do about it?

_No response_

Comece por AssignVMCmd e UserVmManagerImpl, especialmente validateIfVolumesHaveNoSnapshots, validateIfVmHasNoRules e moveVmToUser; depois revise o pull request vinculado #13675. Considera-se concluído quando houver uma explicação clara voltada ao usuário para as falhas de movimentação, em vez de uma exceção não tratada.

Escrita pelo modelo de indexação a partir do texto da issue.