[product-manager-impersonator] Scheduled audit stale-window suppression

## Feature Idea

**Summary:** Add an optional stale-window input to `gh-aw-scheduled-audit` so it skips creating a new report issue when a prior matching issue is still open and recently updated.

## Why a Customer Would Want This
Teams running scheduled detector workflows want actionable signal, not repeated issue churn for findings they are already actively tracking. Today, a daily/weekday schedule can keep re-opening the same conversation before maintainers have had time to act, which adds notification fatigue and triage overhead. A small stale-window gives maintainers control over report cadence without disabling audits.

## Rough Implementation Sketch
- Add a new optional input (for example `min-days-between-reports`, default `0`) in `.github/workflows/gh-aw-scheduled-audit.md` under `workflow_call.inputs`.
- In the existing “List previous findings” path, include `updatedAt` in the GitHub issue query and compute whether the latest matching issue is within the configured window.
- If the newest matching open issue is inside the window, short-circuit to a safe `noop` outcome with a clear reason; otherwise continue with normal detector execution.
- Document the input and behavior in `gh-agent-workflows/scheduled-audit/README.md` and add an example override in `gh-agent-workflows/scheduled-audit/example.yml`.

## Why It Won't Be That Hard
The scheduled-audit workflow already fetches prior findings and already contains duplicate-handling behavior, so this is an incremental extension rather than a new subsystem. The change surface is small (one reusable workflow plus docs/example), and it reuses existing issue-list data flow and safe-output behavior. This should fit in a 1–2 day implementation and validation cycle.

## Evidence
- `.github/workflows/gh-aw-scheduled-audit.md` already has a “List previous findings” step and writes `/tmp/previous-findings.json`, showing prior-report awareness is already built in.
- `.github/workflows/gh-aw-scheduled-audit.md` prompt instructions already reference behavior based on previous findings and replacement mode, so cooldown logic is conceptually adjacent.
- `gh-agent-workflows/scheduled-audit/README.md` documents duplicate-avoidance/close-older behavior, indicating user-facing report-churn control is already part of this workflow’s value proposition.
- Recent repository activity is heavily focused on reliability and operational polish (for example PRs `#1945`, `#1948`, `#1944`), aligning this with current maintenance direction.

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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/33177994241)

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

Start with the “List previous findings” path in .github/workflows/gh-aw-scheduled-audit.md and inspect how /tmp/previous-findings.json and safe-output handling work. Then read gh-agent-workflows/scheduled-audit/README.md and example.yml for the documented interface. Done means the optional window suppresses matching recent open reports with a clear noop reason, while older or absent reports follow the existing path and the documentation includes an override example.

Written by the indexing model from the issue text.