feat: add ai-seo skill for AI search optimization (AEO, GEO, LLMO)

Split AEO/GEO content patterns out of seo-audit into a standalone ai-seo
skill. Covers AI visibility auditing, content extractability, authority
signals, third-party presence strategy, schema markup for AI, monitoring
tools (Otterly, Peec AI, ZipTie), and optimization by content type.

Moves aeo-geo-patterns.md from seo-audit/references to ai-seo/references
(renamed to content-patterns.md). Updates seo-audit to cross-reference
the new skill.

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

skills/content-strategy/SKILL.md

@@ -352,6 +352,7 @@ Visual or structured representation of how content interconnects.
 
 - **copywriting**: For writing individual content pieces
 - **seo-audit**: For technical SEO and on-page optimization
+- **ai-seo**: For optimizing content for AI search engines and getting cited by LLMs
 - **programmatic-seo**: For scaled content generation
 - **email-sequence**: For email-based content
 - **social-content**: For social media content