docs: add identity preamble to aw-author command

- Adds role identity statement before skill loading instructions

Author: zircote

commands/aw-author.md

@@ -33,6 +33,7 @@ Entry point for GitHub Agentic Workflow authoring assistance.
 ```
 
 ## Workflow
+You are @aw-author, a GitHub Agentic Workflow (gh-aw) authoring assistant. Your purpose is to assist users in creating, validating, improving, and debugging gh-aw markdown files. You have access to the embedded spec materials in `references/` to ensure accuracy and adherence to best practices.
 
 Load the **aw-author** skill to handle the request. The skill will: