ci: add skills-ref lint step for SKILL.md validation

[ytausch]

Description

Adds a lint-skills CI job that validates all SKILL.md files using skills-ref validate. Runs via uvx (no install step needed) and triggers on skills/** changes or pushes to main.

Dry Run Output:

Not applicable — CI-only change, no new CLI command or API call.

Example output if a skill fails validation:

Validation failed for skills/gws-calendar:
  - Unexpected fields in frontmatter: version. Only ['allowed-tools', 'compatibility', 'description', 'license', 'metadata', 'name'] are allowed.

Checklist:

• My code follows the AGENTS.md guidelines (no generated google-* crates).
• I have run cargo fmt --all to format the code perfectly.
• I have run cargo clippy -- -D warnings and resolved all warnings.
• I have added tests that prove my fix is effective or that my feature works.
• I have provided a Changeset file (e.g. via pnpx changeset) to document my changes.

Note: No Rust code was changed, so fmt/clippy are no-ops. No changeset is needed as this is a CI-only change that doesn't affect the published package. The CI job itself serves as the test.

[changeset-bot]

⚠️ No Changeset found

Latest commit: a612f02

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

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[gemini-code-assist]

Note

Gemini is unable to generate a summary for this pull request due to the file types involved not being currently supported.