Support Vercel/Skills(skill.sh)

### Is there an existing issue for this?

- [x] I have searched the existing issues

### Feature description

Please support Vercel/Skills(skill.sh)

- https://github.com/vercel-labs/skills
- https://skills.sh/

## skills-lock.json

skills version is managed by `skills-lock.json`

```json
{
"version": 1,
"skills": {
"ios-design-guidelines": {
"source": "ehmo/platform-design-skills",
"sourceType": "github",
"computedHash": "4e61d1d5668179860746145d26b9e17179b4822e012a480d6c077656d0f9d324"
},
"swiftui-expert-skill": {
"source": "AvdLee/SwiftUI-Agent-Skill",
"sourceType": "github",
"computedHash": "cc254d18562b0666f4c85561b92b21eb1878e346b659f8b6d80c02a166725cb4"
}
}
}
```

Start by reviewing the linked Vercel/Skills project and the provided skills-lock.json format, then compare how existing Dependabot ecosystems are structured. Trace how a lockfile source, GitHub skill source, and version are represented. Done means Dependabot can recognize skills-lock.json and produce correct updates for the listed skills.

Written by the indexing model from the issue text.