[WinUI OSS] Triage and close stale GitHub pull requests

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## Summary

Review stale pull requests in the GitHub repository and close, revive, or redirect them based on current WinUI development needs.

## Context

Old pull requests can create uncertainty for contributors and maintainers. Some may still be useful but need rebasing or owner follow-up; others may be obsolete because the affected code, build path, or product direction has changed.

This task should create a repeatable cleanup pattern that is fair to contributors and keeps the active review queue meaningful.

## Work to do

- Identify stale open pull requests and group them by likely action: close, request update, needs maintainer review, or still active.
- Use public comments that explain why a PR is being closed or what is needed to continue.
- Re-label or update PRs that should remain active.
- Capture any recurring causes of PR staleness as follow-up tasks for docs, templates, labels, or automation.
- Coordinate with issue cleanup, label cleanup, and bot/command investigation work.

## Definition of done

- Stale pull requests have been reviewed and dispositioned.
- Contributors receive clear public communication where action is taken.
- The active PR list better reflects current work.
- Follow-up process or automation improvements are tracked separately.

Start in the repository’s open pull request queue and identify stale PRs, grouping each as close, request an update, seek maintainer review, or keep active. Review existing public comments, labels, and related issue, label, and bot work before acting. Done means stale PRs are dispositioned with clear contributor communication, the active queue is more accurate, and follow-up process improvements are recorded separately.

Written by the indexing model from the issue text.