[WinUI OSS] Triage and clean up stale GitHub issues

## Summary

Triage the open GitHub issue backlog so the WinUI repository is easier for maintainers and contributors to use.

## Context

A large or stale issue backlog makes scrum tracking, contributor onboarding, and community engagement harder. This work should identify issues that are obsolete, duplicated, already fixed, no longer actionable, or not aligned with current WinUI development areas.

The cleanup should be done carefully and respectfully: public issues often contain user reports and community context, so closure comments should explain the reason and point contributors to the right next step where possible.

## Work to do

- Define cleanup criteria for stale, obsolete, duplicate, already-fixed, or no-longer-actionable issues.
- Review issues related to older product areas or outdated development paths and decide whether to close, relabel, or move them into a clearer backlog category.
- Identify issue groups that need maintainer review before closure.
- Coordinate with label cleanup and bot/automation tasks so future issue hygiene is easier.
- Use public-safe closure language that avoids internal planning details or private roadmap commitments.

## Definition of done

- A meaningful pass has been completed over stale or outdated GitHub issues.
- Closed issues have clear public explanations.
- Issues that remain open have useful labels or next actions where possible.
- Follow-up automation or policy gaps are tracked separately.