add stale action

[shiva-istari]

Description

This PR adds a scheduled stale-bot workflow (actions/stale@v9) that automatically marks inactive issues and pull requests as stale and closes them if they stay inactive.

How it works

Runs once a day at 02:00 UTC (cron schedule).
An issue or PR with no activity for 60 days is labeled Stale and a comment is posted.
After being marked stale, there is a 7-day cooling period: commenting (or any activity) removes the label and resets the timer; otherwise the item is closed automatically.

Comment posted on stale items

Issues

This issue has been stale for 60 days and will be closed automatically in 7 days. Comment to keep it open.

Pull requests

This PR has been stale for 60 days and will be closed automatically in 7 days. Comment to keep it open.

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