Mark draft PRs as stale after 7 days, close after 7 more

[devin-ai-integration]

Adds two custom gh-based steps to the stale workflow to handle draft PRs on a faster schedule than the default 14/14 day cycle:

• Mark stale draft PRs: Finds open draft PRs with no activity for 7 days and applies the status:stale label with a comment.
• Close stale draft PRs: Finds draft PRs already labeled status:stale with no activity for 7 more days, comments, and closes them.

Both steps respect the existing status:exempt label. The actions/stale step continues to handle non-draft PRs on the existing 14-day schedule. Since actions/stale doesn't support filtering by draft status natively, the custom steps use gh pr list --draft with jq filters instead.

Things to verify in review:

• The jq inside filter used for the "not already stale" check — consider whether any(. == "status:stale") | not would be clearer and more robust (especially for PRs with no labels, where inside may behave unexpectedly).
• Whether draft PRs should be explicitly excluded from the actions/stale step to avoid any overlap in processing.
• updatedAt resets when the stale label is added via gh pr edit, which is what makes the 7-day close window work — worth confirming this assumption.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
  • N/A — workflow-only change, not testable via unit tests
• If this pull request removes docs files, it includes redirect settings in mint.json.
  • N/A
• If this pull request adds functions or classes, it includes helpful docstrings.
  • N/A

Link to Devin session: https://app.devin.ai/sessions/d481a0da7f704d28b2893aa40c454d83
Requested by: @desertaxle

[devin-ai-integration]

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