Add a /skills check command

[dgkanatsios]

Describe the feature or problem you'd like to solve

Command to check the skills folders and understand if they are included today

Proposed solution

My skills weren't included because they had an underscore in their name, which apparently is not allowed by the spec https://agentskills.io/specification
It was unclear why they weren't included though, so Sebastien Ros made a nice suggestion to add a /skills check command to diagnose the issue and provide some feedback.

Example prompts or workflows

No response

Additional context

No response

[schwebke]

I also think this would be helpful to have this as status. Meanwhile I use this workaround:

❯ What agentskills do you see in your context?

◐ The user is asking about agent skills visible in my context. I can see from the system prompt that there's an `<available_skills>` section.

● Based on my context, I can see one available skill:

   - technology-consistency — Checks a project for consistent usage of a technology.

[examon]

This appears to be addressed via /skills list, which now reports skill-loading errors and warnings with file paths and human-readable failure reasons. The underscore naming issue that previously prevented some skills from loading has also been fixed. There is not a separate /skills check subcommand, but the diagnostic behavior is available through /skills list. If you believe this isn't resolved, please feel free to reopen this issue.