[Ubuntu 26.04][Sandbox] multi-gateway status omits owning-gateway recovery target

## Description

On a multi-gateway host, running status or recovery for a sandbox whose owning gateway is unavailable from a healthy default gateway reports only that the sandbox does not exist. It does not name the recorded owning gateway or the recovery target, so the user cannot tell which gateway must be restored or selected.

Platform scope: Reproduced on Ubuntu 26.04 only; other platforms not yet verified with the same multi-gateway setup.
Regression: Unknown — earlier versions not tested
OpenShell issue: No

## Environment

```text
Device: Ubuntu GPU runner
OS: Ubuntu 26.04 / Linux 7.0.0-22-generic
Architecture: x86_64
Node.js: v22.23.1
npm: 10.9.8
Docker: Docker Engine 29.6.1
OpenShell CLI: openshell 0.0.106
NemoClaw: v0.0.116
OpenClaw: 2026.7.1
```

## Steps to Reproduce

1. Install NemoClaw v0.0.116 on an Ubuntu 26.04 host with Docker.
2. Register two disposable OpenClaw sandboxes owned by different NemoClaw gateways, for example failure-a on gateway A and healthy-b on gateway B.
3. Confirm both sandboxes are initially Ready.
4. Stop or suspend only gateway A, leaving gateway B healthy and selected as the default gateway.
5. Run: nemoclaw failure-a status
6. Run: nemoclaw failure-a recover

## Expected Result

The commands exit nonzero and report the failure against sandbox failure-a's owning gateway. The diagnostic should name the owning gateway or its port and should not imply that the sandbox is simply unknown to NemoClaw.

## Actual Result

The commands exit nonzero, but the output says sandbox failure-a does not exist and only lists the sandbox registered on the healthy default gateway. It omits the owning gateway recovery target for failure-a.

## Logs

```text
Expected pattern:
owning gateway name or owning gateway port

Actual output excerpt:
Sandbox 'failure-a' does not exist.

Registered sandboxes: healthy-b
Run 'nemoclaw list' to see all sandboxes.
Sandbox 'failure-a' does not exist.

Registered sandboxes: healthy-b
Run 'nemoclaw list' to see all sandboxes.
```