Promote a local Claude Code skill (from `~/.claude/skills/`, the current project's `.claude/skills/`, or an explicit path) into a Claude Code marketplace repo as a plugin, generating `plugin.json`, updating `marketplace.json` + README, then committing and pushing to GitHub. Also handles updates to already-published skills. Use when the user says "publish skill X", "push my skill to marketplace", "promote local skill", or invokes `/publish-skill <name>`.
