[product-manager-impersonator] Inline `with` starter snippets in workflow examples

## Feature Idea

**Summary:** Add standardized commented `with:` starter snippets to workflow `example.yml` files that currently lack them, so users can configure key inputs directly in the copied trigger file.

## Why a Customer Would Want This
Users are instructed to copy `gh-agent-workflows/*/example.yml` into their repos, but many examples provide no inline hints about which inputs to tune first. That forces context switching to README tables and increases setup mistakes for scheduled workflows. A consistent inline starter block makes first-run setup faster and more reliable, especially for teams adopting multiple workflows at once.

## Rough Implementation Sketch
- Add a short commented `with:` block (2–4 high-impact inputs) to examples that currently have no `with:` guidance.
- Reuse existing style already present in examples like `issue-triage` and `text-auditor` so formatting stays consistent.
- Start with top-recommended and high-adoption workflows, then expand to remaining public workflows.
- Add a lightweight lint/check that every public `example.yml` has either concrete `with:` values or commented starter guidance.

## Why It Won't Be That Hard
This is mostly documentation/template hygiene in plain YAML example files, with no runtime behavior changes to compiled workflows. The pattern already exists in-repo, so implementation is mostly repeatable copy-adapt work rather than net-new design. Scope is small and incremental: one pass over examples plus a simple validation check.

## Evidence
- `gh-agent-workflows/DEVELOPING.md:205` says consumers copy `example.yml` and customize `with:` inputs.
- `gh-agent-workflows/pr-review/example.yml:1-19` has no `with:` guidance, while configurable inputs exist in `gh-agent-workflows/pr-review/README.md:25-35`.
- `gh-agent-workflows/product-manager-impersonator/example.yml:1-17` has no `with:` guidance, while configurable inputs exist in `gh-agent-workflows/product-manager-impersonator/README.md:28-39`.
- `gh-agent-workflows/docs-patrol/example.yml:1-17` has no `with:` guidance.
- Existing positive pattern: `gh-agent-workflows/issue-triage/example.yml:17-29` and `gh-agent-workflows/text-auditor/example.yml:17-23` include commented starter configuration blocks.

## Suggested Actions
- [ ] Add standardized commented `with:` starter snippets to public workflow examples that currently omit them.
- [ ] Keep snippet style consistent with existing examples (`issue-triage`, `text-auditor`).
- [ ] Add a lightweight repo check to prevent future examples from missing starter guidance.

---
[What is this?](https://ela.st/github-ai-tools) | [From workflow: Trigger Product Manager Impersonator](https://github.com/elastic/ai-github-actions/actions/runs/30445279367)

Give us feedback! React with 🚀 if perfect, 👍 if helpful, 👎 if not.

Read gh-agent-workflows/DEVELOPING.md:205, then compare examples such as issue-triage/example.yml and text-auditor/example.yml with pr-review, product-manager-impersonator, and docs-patrol and their README input tables. Identify public examples without guidance and define the lightweight check from the existing pattern. Done means each public example has concrete with: values or a consistent commented starter block, with the check passing.

Written by the indexing model from the issue text.