[NemoHermes][Gemini][Regression] v0.0.124 provider validation fails with Chat Completions HTTP 400

> [!WARNING]
> **Regression** — the Gemini provider-validation failure previously tracked in #11141 recurs on NemoClaw v0.0.124.

## Description

Non-interactive NemoHermes onboarding reaches provider validation in a healthy environment, but the Gemini Chat Completions probe returns HTTP 400. Onboarding aborts before sandbox creation and before the tool-schema acceptance test can execute.

Platform scope: Reproduced independently on Ubuntu 24.04 x86_64 and DGX Spark aarch64.

Related: #11141 reported the same validation signature on an earlier release and is closed as completed. This issue tracks its recurrence on v0.0.124 without reopening the completed issue.

## Environment

```text
NemoClaw: v0.0.124
OpenShell: v0.0.116
Agent/runtime: NemoHermes
Provider: Google Gemini
Execution mode: non-interactive onboarding
```

## Steps to Reproduce

1. Start from a clean environment with a valid configured Gemini credential.
2. Run non-interactive NemoHermes onboarding with the Gemini provider.
3. Observe live provider validation.

## Expected Result

Provider validation succeeds for the supported Gemini configuration and onboarding proceeds to sandbox creation.

## Actual Result

Docker and OpenShell preconditions pass, but the Gemini Chat Completions validation probe returns HTTP 400 and onboarding aborts.

## Impact

Gemini-backed NemoHermes onboarding and strict tool-schema validation cannot run on the affected platforms.

## Logs

```text
Provider validation failed: Chat Completions request returned HTTP 400.
Onboarding stopped before sandbox creation.
```

Start by reproducing non-interactive NemoHermes onboarding with a valid Gemini credential on one of the reported platforms, then trace the provider-validation Chat Completions probe that returns HTTP 400. Compare the v0.0.124 behavior with the earlier regression in #11141; done means supported Gemini validation succeeds and onboarding reaches sandbox creation and tool-schema testing.

Written by the indexing model from the issue text.