Add dotnet-maui-doctor skill and refs

[Redth]

Add a new .agents/skills/dotnet-maui-doctor skill bundle. Includes SKILL.md describing an autonomous workflow to detect and remediate .NET MAUI environment issues and platform-specific reference docs for installation commands, platform requirements, troubleshooting, Microsoft OpenJDK guidance, and a WorkloadDependencies discovery guide that pulls authoritative versions from NuGet. Documents validation/remediation steps for .NET SDK, workloads, JDK, Android SDK, Xcode, and Windows SDK (macOS/Windows/Linux).

Skill Validation Results: dotnet-maui-doctor

#	Check	Result
1	Skill name matches directory name	✅ dotnet-maui-doctor = directory name
2	Skill name is lowercase with hyphens only	✅ dotnet-maui-doctor — all lowercase, hyphens only
3	Description is non-empty and under 1024 chars	✅ 505 chars (limit: 1024)
4	SKILL.md body is under 500 lines	✅ 160 lines (limit: 500)
5	Instructions are specific and actionable	✅ Tasks include concrete bash/powershell commands, specific URLs, and clear rules
6	Workflow has numbered steps with clear checkpoints	✅ 10 numbered tasks with specific validation criteria per step
7	Validation section exists with observable success criteria	✅ Validation section with 6 observable criteria + build verification + optional run verification
8	No secrets, tokens, or internal URLs	✅ None found

All 8 validation checks pass.

[jeffschwMSFT]

thanks @Redth for this skill. can you run it through the skill validator and share the results?

[Redth]

@jeffschwMSFT I updated the PR description with the results

[jeffschwMSFT]

thanks @Redth, which evaluator did you use? was this a with and without skill evaluation? the default evaluator is under eng/skill-validator

[Redth]

Ahhh i didn't see the eng/ stuff, I will give that a go, thanks :)

[timheuer]

@Redth location is wrong -- can you create dotnet-maui plugin structure and put skills there -- this would be the way to be able to create the plugin landing spot for this and other MAUI skills.

[Redth]

Yeah @jfversluis and I are going to talk about setting this up in a dotnet-maui plugin now in the repo here.

I also would be curious to see thoughts on how to apply assertions and validation to this one in particular - it's going to require having a workflow image in a 'broken' state intentionally (which I'm not sure we can do without first running something deterministic to remove the baseline installed things, only to then try and run the skill and assert that it fixes the environment up - this may be a viable route, but it could also be a rather poor test too).

Any thoughts on that @timheuer or @jeffschwMSFT ?

[ViktorHofer]

Closing PR of age as we changed the repository structure since (and made the repo public which caused a disconnection to forked repos). If you still want to get this in, please submit a new PR.