[DGX Station][Agent&Skills] Google Chat channel setup rejects any real service-account credential — "must not contain line breaks"

## Description

Setting up the Google Chat messaging channel — either during the onboard wizard or via the standalone `channels add googlechat` command — fails immediately with `Messaging input values must not contain line breaks.` for any real Google Chat service-account credential. A standard Google Cloud service-account JSON key legitimately contains embedded newlines (most commonly inside the `private_key` field, or simply because the JSON is pretty-printed), so this rejects every real-world Google Chat credential and makes the channel impossible to configure through any documented path.

**Platform scope:** Reproduced on DGX Station GB300; the failure is in a generic messaging-input validator shared across channel setup, so it is very likely platform-independent — not independently verified on another platform.

**Regression:** Unknown — not separately tested on an earlier version.

## Environment

```text
Device: DGX Station GB300
OS: Ubuntu 24.04 (DGX OS)
Architecture: aarch64
Node.js: v22.23.2
npm: 10.9.8
Docker: 29.2.1
OpenShell CLI: 0.0.106
NemoClaw: v0.0.114
OpenClaw: 2026.7.1
```

## Steps to Reproduce

1. Prepare a real Google Cloud service-account JSON key (the standard credential type Google Chat integrations require) and export it as `GOOGLECHAT_SERVICE_ACCOUNT`, along with `GOOGLECHAT_AUDIENCE` and `GOOGLECHAT_APP_PRINCIPAL`, exactly as documented.
2. On an existing sandbox, run:
```bash
nemoclaw {sandbox} channels add googlechat
```
(or select googlechat during the `nemoclaw onboard` wizard's messaging-channel step)

## Expected Result

Google Chat channel setup accepts the service-account credential (embedded newlines and all, since that is the standard shape of this credential type) and completes successfully, registering the channel the same way Discord, Slack, or Telegram already do.

## Actual Result

Setup fails immediately, before any interactive prompt is even shown:

```text
Failed to plan messaging channel 'googlechat'.
Messaging input values must not contain line breaks.
```

This reproduces identically whether attempted through the onboard wizard's channel checkbox or the standalone channels-add command, and regardless of what other channels are also being configured at the same time — confirming the failure is specific to Google Chat credential handling itself, not an interaction with another channel. Google Chat cannot be configured on any sandbox through any documented path while using a real, standard-format service-account key.

## Logs

```text
$ nemoclaw openclaw-up channels add googlechat
Effective egress that would be opened:
policy 'googlechat':
- chat.googleapis.com:443 (protocol: rest, enforcement: enforce)
- www.googleapis.com:443 (protocol: rest, enforcement: enforce)
Failed to plan messaging channel 'googlechat'.
Messaging input values must not contain line breaks.
```