Suggested test: copilot/label-command

## Motivation

github/gh-aw#41920 — `Add run-again footer hints for slash and label command triggers` — adds footer rendering for `label_command` triggers and emits `GH_AW_LABEL_COMMANDS` in the compiled workflow. The `label_command` trigger type has **no E2E test** in `githubnext/gh-aw-test`; only `slash_command` is currently exercised via `test-copilot-command.md`.

## Proposed test

- **Workflow file**: `test-copilot-label-command.md`
- **Trigger**: `label_command:` (label added to an issue)
- **Engine**: copilot
- **Safe output**: `add-comment`
- **Variant**: standard

## Minimal test prompt sketch

When the label `test-copilot-label-command` is added to an issue, reply to that issue with a comment from Copilot that acknowledges the label was applied and writes a haiku about the repo. This exercises the `label_command` trigger path and verifies the compiled workflow fires on label events.

## New fixtures or secrets needed

None — the harness already creates issues and can add labels via `gh issue edit --add-label`. The label `test-copilot-label-command` would need to exist in the repo (pre-created as part of the test setup, similar to how issue-triggered tests work). `e2e.sh` would also need a new `label-command` trigger category (analogous to the `*command` case) that adds the label instead of posting a slash command comment.

## Notes

`test-copilot-command.md` covers `slash_command` but not `label_command`. The two trigger types share the same compiled output structure but differ in how the harness fires them and how `GH_AW_LABEL_COMMANDS` vs. `GH_AW_SLASH_COMMANDS` are set. Adding this test would complete the command-trigger coverage. The footer hint for label commands (added in gh-aw#41920) is incidentally validated when the `add-comment` safe output fires with the expected footer.

> Generated by [🔍 Suggest New E2E Tests](https://github.com/githubnext/gh-aw-test/actions/runs/28318008590) · 110.8 AIC · ⌖ 11.6 AIC · ⊞ 5.9K · [◷](https://github.com/search?q=repo%3Agithubnext%2Fgh-aw-test+is%3Aissue+%22gh-aw-workflow-call-id%3A+githubnext%2Fgh-aw-test%2Fsuggest-new-e2e-tests%22&type=issues)