Add performance best practices guide

[davidortinau]

Summary

Adds a comprehensive performance best practices guide for .NET MAUI applications.

Split from #3202 — this guide document stands on its own merit independent of the llms.txt initiative and should be reviewed/merged separately.

Content

Covers startup performance, layout optimization, binding overhead, image handling, and platform-specific tuning guidance.

Co-authored-by: Gerald Versluis gerald.versluis@microsoft.com

[learn-build-service-prod]

Learn Build status updates of commit 613a458:

⚠️ Validation status: warnings

File	Status	Preview URL	Details
docs/deployment/performance-best-practices.md	⚠️Warning	View (>=net-maui-8.0)	Details

docs/deployment/performance-best-practices.md

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[learn-build-service-prod]

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[learn-build-service-prod]

PoliCheck Scan Report

The following report lists PoliCheck issues in PR files. Before you merge the PR, you must fix all severity-1 and severity-2 issues. The AI Review Details column lists suggestions for either removing or replacing the terms. If you find a false positive result, mention it in a PR comment and include this text: #policheck-false-positive. This feedback helps reduce false positives in future scans.

✅ No issues found

More information about PoliCheck

Information: PoliCheck | Severity Guidance | Term
For any questions: Try searching the learn.microsoft.com contributor guides or post your question in the Learn support channel.

[learn-build-service-prod]

Learn Build status updates of commit e11c47a:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/deployment/performance-best-practices.md	✅Succeeded	View (>=net-maui-8.0)

For more details, please refer to the build report.

[jfversluis]

This can be closed, was taken from the llms.txt PR but has a lot, if not all, overlap with existing content.