[WinUI OSS] Research GitHub-to-build integration patterns

## Summary

Research public repository to build-system integration patterns used by projects such as Terminal and PowerToys, and summarize what applies to WinUI.

## Context

Terminal and PowerToys are useful comparison points because they operate as public GitHub projects with build and validation workflows that may need downstream integration. This task should capture reusable patterns without copying private implementation details.

## Work to do

- Review public GitHub workflows, docs, and repository layout patterns from comparable projects.
- Identify how source synchronization, PR validation, and scheduled builds are represented.
- Note patterns WinUI should reuse or avoid.
- Turn findings into follow-up tasks for WinUI build and validation readiness.
- Avoid private conversations, private pipeline links, or non-public operational details.

## Definition of done

- Comparable project patterns are summarized.
- WinUI-relevant recommendations are documented.
- Follow-up implementation work is identified.
- Findings are safe to discuss in public issue context.