Initial release of the glab skill based on @steipete gh skill.

• Enables interaction with GitLab via the glab CLI for merge requests, CI/CD pipelines, issues, releases, and API queries.
• Supports both gitlab.com and self-hosted GitLab instances.
• Allows advanced API usage (REST and GraphQL) and JSON output piping for automation.
• Includes key workflow commands with examples for MR handling, CI/CD operations, issue management, and release creation.
• Documents key differences between glab and GitHub CLI for smoother onboarding.