ci(e2e): Brave Search jobs start without BRAVE_API_KEY

Parent: #9159

## Problem

Selected Brave Search E2E jobs start without `BRAVE_API_KEY`. The live tests skip during prerequisite checks. The target runner then fails because no test ran.

No OpenClaw or Brave Search product behavior executes. The resulting failures look like two test failures, but they have one configuration cause.

## Recent evidence

| Main E2E run | Commit SHA | Failed jobs | Observed result |
| --- | --- | --- | --- |
| [32178707220](https://github.com/NVIDIA/NemoClaw/actions/runs/32178707220) | `b2d1ce52a716444b083f6e3b8ed8bace1cba3240` | [balanced egress](https://github.com/NVIDIA/NemoClaw/actions/runs/32178707220/job/95856131529), [Brave Search](https://github.com/NVIDIA/NemoClaw/actions/runs/32178707220/job/95856132076) | `BRAVE_API_KEY` is empty; both tests skip; the runner reports that no tests ran. |
| [32109011388](https://github.com/NVIDIA/NemoClaw/actions/runs/32109011388) | `e19eff8d623ffa0bb9d0acc1afe4e4c809416d43` | [Brave Search](https://github.com/NVIDIA/NemoClaw/actions/runs/32109011388/job/95624846200), [balanced egress](https://github.com/NVIDIA/NemoClaw/actions/runs/32109011388/job/95624846206) | Same empty credential and no-tests signature. |
| [32101603265](https://github.com/NVIDIA/NemoClaw/actions/runs/32101603265) | `c0b1862fcb65dd0b568e29e0fa111d710c6b0783` | [Brave Search](https://github.com/NVIDIA/NemoClaw/actions/runs/32101603265/job/95604179031), [balanced egress](https://github.com/NVIDIA/NemoClaw/actions/runs/32101603265/job/95604179242) | Both jobs failed together. |

At `b2d1ce52`, `.github/workflows/e2e.yaml` passes `secrets.BRAVE_API_KEY` to the `catalogue-brave-nvidia-inference` reusable workflow. The job environment shows an empty `BRAVE_API_KEY` and an available `NVIDIA_INFERENCE_API_KEY`.

The evidence does not show whether the Brave Search API key was deleted, renamed, or made unavailable by GitHub secret scope.

## Classification

- Configuration or authentication failure.
- Recurring and deterministic while the required credential is unavailable.
- Not eligible for retry. A missing required credential is terminal.
- No current issue or PR owns the failure signature.

## Required outcome

- Identify the GitHub secret location and maintainer responsible for `BRAVE_API_KEY` availability.
- Restore the credential path or correct the workflow binding without exposing the API key.
- If a selected Brave Search E2E job lacks the credential, fail during a named preflight step before the live test starts.
- Preserve the existing release result: missing required Brave Search evidence remains a failure.
- Keep logs and artifacts free of credential material.
- Add deterministic evidence for the missing-credential classification when source changes are required.
- Verify that both selected jobs execute product behavior on one exact commit SHA.

## Non-goals

- Retry the live tests or the complete workflow.
- Convert the missing credential into a skip or passing result.
- Remove either E2E behavior contract.