feat: Add MAUI Expert agent for .NET cross-platform app development

[PureWeen]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

---

Description

Summary

Adds a comprehensive .NET MAUI Expert agent and updates the associated instructions file to provide accurate, up-to-date guidance for cross-platform mobile and desktop development with .NET MAUI.

Changes

New Agent: agents/dotnet-maui.agent.md

A specialized agent for .NET MAUI development that provides:

• Critical Rules — Enforces modern MAUI patterns (e.g., CollectionView over ListView, Border over Frame, Grid over *AndExpand)
• Control Reference — Quick lookup tables for deprecated controls and their replacements
• Shell Navigation — Best practices for route registration and GoToAsync patterns
• Performance Guidelines — Layout optimization, compiled bindings, image handling
• Common Pitfalls — Proactive warnings about frequent MAUI migration mistakes

Updated: instructions/dotnet-maui.instructions.md

Synced with the agent's guidance and validated against Microsoft Learn documentation:

• Added Layout and Control Selection section
• Added Shell Navigation guidance
• Added Resources and Assets best practices
• Clarified Dispatcher vs MainThread threading APIs (prefer IDispatcher injection or BindableObject.Dispatcher)
• Removed stale/non-MAUI content (BatchBegin/BatchCommit, generic caching strategies)

Validation

All guidance was cross-referenced with official Microsoft Learn documentation to ensure accuracy:

• ListView/TableView deprecation confirmed
• Frame → Border migration confirmed
• *AndExpand obsolescence confirmed
• VerticalStackLayout/HorizontalStackLayout performance benefits confirmed
• Dispatcher API recommendations validated

---

Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• New collection file.
• Update to existing instruction, prompt, chat mode, or collection.
• Other (please specify): Agent

---

Additional Notes

---

By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull request overview

This PR adds a comprehensive .NET MAUI Expert agent and updates the associated instructions file to provide modern, best-practice guidance for cross-platform mobile and desktop development with .NET MAUI. The changes enforce deprecated API avoidance (ListView, TableView, Frame, BackgroundColor) and promote modern alternatives (CollectionView, Border, Background property), along with performance optimizations like compiled bindings and proper layout practices.

Key Changes:

• New MAUI Expert agent with critical rules, control references, and best practices
• Updated instructions file with enhanced guidance on layouts, Shell navigation, threading APIs, and common pitfalls
• README entry added in proper alphabetical order

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
agents/dotnet-maui.agent.md	New comprehensive MAUI expert agent with critical rules, control reference tables, compiled bindings guidance, and handler customization patterns
instructions/dotnet-maui.instructions.md	Updated with critical rules for deprecated APIs, enhanced dispatcher/threading guidance, Shell navigation patterns, and common pitfalls section
docs/README.agents.md	Added MAUI Expert entry in correct alphabetical position between Lingo.dev and Mentor agents