Add Whitewind blog post creation tool
- Create new tool for posting to Whitewind using com.whtwnd.blog.entry lexicon
- Support title, content (markdown), and optional subtitle
- Hardcode theme as github-light and visibility as public
- Generate proper Whitewind URLs (https://whtwnd.com/{handle}/entries/{rkey})
- Follow existing pattern of using environment variables for credentials
🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>