Adds commands/ directory with 7 top content commands that appear in the UI
Customize sidebar: create-content, content-brief, social-adapt, publish,
translate, brand-setup, audit-content. Each follows Anthropic's command
format with frontmatter, detailed instructions, and follow-up suggestions.
Version bumped to 3.1.0.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>