Add required name field to skills frontmatter

[krubenok]

Per the Agent Skills specs, a name and a description field are both required in the frontmatter of a SKILL.md file.

In Claude Code, it seems like the required name field is not being enforced, but after installing the skills in codex, I would get the following error:

⚠ Skipped loading 3 skill(s) due to invalid SKILL.md files.

⚠ /Users/kyrubeno/.codex/skills/ruff/SKILL.md: invalid YAML: missing field `name`

⚠ /Users/kyrubeno/.codex/skills/ty/SKILL.md: invalid YAML: missing field `name`

⚠ /Users/kyrubeno/.codex/skills/uv/SKILL.md: invalid YAML: missing field `name`

This was confirmed as well with the skills-ref validate CLI (which itself is perhaps a good candidate to run in CI alongside the Prettier issue in #2)

 ❯ skills-ref validate /Users/kyrubeno/Developer/Personal/claude-code-plugins/plugins/astral/skills/uv
Validation failed for /Users/kyrubeno/Developer/Personal/claude-code-plugins/plugins/astral/skills/uv:
  - Missing required field in frontmatter: name

After the changes, the skills load without issue in Codex and pass the validator. I also added the optional author and license metadata which helped me distinguish this from a similarly named skill I had written myself before and a small correction to the CONTRIBUTING.md file. Per the specs the metadata fields should not be provided to the models so it's purely organizational.

[Conor-McLeod]

Please merge this! Can't install with vercel-labs/skills CLI until the frontmatters are fixed.

[krubenok]

@zanieb hopefully this is a pretty easy one to merge if you have a moment to take a look. Totally forgot about this PR thanks Conor 👍

[zanieb]

This seems unrelated. This is after cloning without changing directories so the path won't work. The current example worked for me.

[krubenok]

Weird. I can still repro the original version not working. Edit: slightly dense moment

I think the patch is correct since the intent is to add the local instance of the marketplace and the folder in the repo is indeed called claude-plugin The detail is in the examples from Claude's error output;

Examples:
• owner/repo (GitHub)
• git@github.com:owner/repo.git (SSH)
• https://example.com/marketplace.json
• /path/to/marketplace

Since contributors to the repo should use the local one, a relative path is appropriate, but general consumption should use /plugin marketplace add astral-sh/claude-code-plugins to get the latest from GitHub.