[product-manager-impersonator] Comment workflow outputs for chaining

## Feature Idea

**Summary:** Add `workflow_call` outputs for comment-creation workflows (starting with `Create Comment On Issue`) so callers can chain follow-up jobs using `created_comment_id` and `created_comment_url`.

## Why a Customer Would Want This
Teams are increasingly chaining workflows in one run. Today they can branch on `created_issue_*` and `created_pr_*`, but comment-only workflows have no equivalent output contract, so downstream orchestration (notifications, metrics, conditional follow-ups) becomes brittle and indirect.

## Rough Implementation Sketch
- Add `on.workflow_call.outputs` to `.github/workflows/gh-aw-create-comment-on-issue.md` for `created_comment_id` and `created_comment_url`.
- Propagate `safe-outputs.add-comment` result fields from the conclusion job into those outputs (same pattern used for issue/PR outputs).
- Recompile lock files and document new outputs in `gh-agent-workflows/create-comment-on-issue/README.md`.
- Extend chaining docs with a small example showing `if: needs.comment.outputs.created_comment_id != ''`.

## Why It Won't Be That Hard
The repository already has a proven output-propagation pattern for safe outputs (`created_issue_*`, `created_pr_*`). This is mostly wiring one additional safe-output type into the same workflow-call output surface plus docs updates.

## Evidence
- `.github/workflows/gh-aw-create-comment-on-issue.md:21-55` defines `workflow_call` inputs/secrets but no outputs.
- `.github/workflows/gh-aw-create-comment-on-issue.md:73-79` already configures `safe-outputs.add-comment`, so output source data is naturally colocated.
- `docs/workflows/detector-fixer-chaining.md:11-17` documents only `created_issue_number` / `created_issue_url` output contracts.
- `docs/upgrading.md:11-12` highlights safe-output workflow outputs only for issue/PR creation, not comment creation.

> [!NOTE]
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> 🔒 Integrity filtering filtered 32 items
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> Integrity filtering activated and filtered the following items during workflow execution.
> This happens when a tool call accesses a resource that does not meet the required integrity or secrecy level of the workflow.
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> - issue:elastic/ai-github-actions#765 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#849 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#848 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#847 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#823 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#840 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#841 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#839 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#838 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#837 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#835 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#833 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#831 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#830 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#829 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - issue:elastic/ai-github-actions#828 (`list_issues`: has lower integrity than agent requires. The agent cannot read data with integrity below "approved".)
> - ... and 16 more items
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[What is this?](https://ela.st/github-ai-tools) | [From workflow: Trigger Product Manager Impersonator](https://github.com/elastic/ai-github-actions/actions/runs/23843850211)

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