feat: add grok.com site support (#60)

Add support for grok.com site with two commands:
- ask: Send a message to Grok and get response
- debug: Debug grok page structure

Implementation uses Playwright CDP protocol with fallback DOM selectors
(div.message-bubble, [data-testid="message-bubble"]) for reliability.

Co-authored-by: xdord <xdord@xdorddeMac-mini.local>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>