Add test-copilot-harness-watchdog-timeout for engine.harness.watchdog-timeout-ms

> [!CAUTION]
> Protected files were modified in this change.
> This pull request is in `request_review` mode and requires explicit human scrutiny before merge.
>
> Protected files: `.github/workflows/test-copilot-harness-watchdog-timeout.md`

## Motivation

github/gh-aw#51292 raised the default post-result harness watchdog idle timeout from 20s to 120s and added a new frontmatter field `engine.harness.watchdog-timeout-ms` (compiling to `GH_AW_HARNESS_WATCHDOG_TIMEOUT_MS`) so workflows can tune the timeout per-workflow. This behavior had no dedicated E2E regression coverage.

## Test added

- **Workflow file**: `test-copilot-harness-watchdog-timeout.md`
- **Trigger**: `workflow_dispatch`
- **Engine**: copilot
- **Safe output**: `create-issue`
- **Variant**: standard

Sets `engine.harness.watchdog-timeout-ms: 120000` in frontmatter and creates an issue via the sample, exercising the compiler's parsing/injection of the new field end-to-end (the value flows into `GH_AW_HARNESS_WATCHDOG_TIMEOUT_MS` env for the harness). Uses a `samples:` block so it runs deterministically with `--use-samples`.

## Notes

I could not run `gh aw compile` in this sandbox (the `gh-aw` extension isn't installed here), so no `.lock.yml` is included — per repo convention the lockfile is regenerated by `gh aw compile .github/workflows/test-copilot-harness-watchdog-timeout.md` before merge/first run.

> Generated by [🔍 Suggest New E2E Tests](https://github.com/githubnext/gh-aw-test/actions/runs/31248948064) · auto · 53.2 AIC · ⌖ 10.2 AIC · ⊞ 8.3K · [◷](https://github.com/search?q=repo%3Agithubnext%2Fgh-aw-test+%22gh-aw-workflow-id%3A+suggest-new-e2e-tests%22&type=pullrequests)

---

> [!NOTE]
> This was originally intended as a pull request, but the git push operation failed.
>
> **Original error:** pushSignedCommits: refusing unsigned push for branch 'test-copilot-harness-watchdog-timeout-d9aa382e57979a42': Signed-commit payload violates file-protection policy (request_review): .github/workflows/test-copilot-harness-watchdog-timeout.md
>
> **Workflow Run:** [View run details and download bundle artifact](https://github.com/githubnext/gh-aw-test/actions/runs/31248948064)
>
> The bundle file is available in the `agent` artifact in the workflow run linked above.

To create a pull request with the changes:

```sh
# Download the artifact from the workflow run
gh run download 31248948064 -n agent -D /tmp/agent-31248948064

# Fetch the bundle into a temporary ref, then update the local branch
git fetch /tmp/agent-31248948064/aw-test-copilot-harness-watchdog-timeout.bundle refs/heads/test-copilot-harness-watchdog-timeout:refs/bundles/create-pr-test-copilot-harness-watchdog-timeout-d9aa382e57979a42-ea2f3140
git update-ref refs/heads/test-copilot-harness-watchdog-timeout-d9aa382e57979a42 refs/bundles/create-pr-test-copilot-harness-watchdog-timeout-d9aa382e57979a42-ea2f3140
git checkout test-copilot-harness-watchdog-timeout-d9aa382e57979a42
# Ensure the working tree matches the updated branch
git reset --hard
# Remove the temporary bundle ref
git update-ref -d refs/bundles/create-pr-test-copilot-harness-watchdog-timeout-d9aa382e57979a42-ea2f3140

# Push the branch to origin
git push origin test-copilot-harness-watchdog-timeout-d9aa382e57979a42

# Create the pull request
gh pr create --title 'Add test-copilot-harness-watchdog-timeout for engine.harness.watchdog-timeout-ms' --base main --head test-copilot-harness-watchdog-timeout-d9aa382e57979a42 --repo githubnext/gh-aw-test
```

Start with .github/workflows/test-copilot-harness-watchdog-timeout.md and the linked workflow-run bundle, then review the samples block and run `gh aw compile .github/workflows/test-copilot-harness-watchdog-timeout.md`. Done means the workflow covers the watchdog-timeout frontmatter end to end, its lockfile is regenerated, and the E2E run succeeds.

Written by the indexing model from the issue text.