ci: add stale issue workflow

[efiop]

Summary

• Adds a scheduled/manual stale issue workflow using actions/stale@v10.
• Adds an actions/github-script@v9 sync step that labels issues awaiting user response only when the latest non-bot issue comment is from a maintainer (OWNER, MEMBER, or COLLABORATOR).
• Configures stale processing to never select issues on its own and to close only issues already labeled awaiting user response after 14 days with no activity.
• Disables PR stale handling and removes awaiting user response when the latest non-bot issue comment is not from a maintainer.

Validation

• PATH=/Users/efiop/.local/bin:$PATH /Users/efiop/.local/bin/pre-commit run --all-files

Notes

• Confirmed actions/stale is the GitHub-owned action; GitHub Docs use actions/stale@v10 for closing inactive issues.
• The maintainer gate uses GitHub issue comment author_association values exposed by the Issues API.