Add dedicated sync workflow for Claude skill

[developersdigest]

Summary

• add a workflow that syncs the CLI firecrawl skill directly into the Claude plugin repo and automatically creates/merges sync PRs
• rename the existing plugin sync workflow to clarify it only handles plugin config, and switch it to reuse the existing FIRECRAWL_SKILLS_SYNC secret
• add a small documentation note to the Firecrawl CLI skill to help detect branch triggers during sync testing

Testing

• Not run (not requested)