feat: add site-architecture skill for website structure planning

Fills the gap between content strategy and SEO skills — covers page
hierarchy, navigation design, URL structure, and internal linking.

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

.claude-plugin/marketplace.json

@@ -12,7 +12,7 @@
   "plugins": [
     {
       "name": "marketing-skills",
-      "description": "29 marketing skills for technical marketers and founders: CRO, copywriting, cold email, SEO, AI SEO, paid ads, ad creative, churn prevention, pricing strategy, referral programs, and more",
+      "description": "30 marketing skills for technical marketers and founders: CRO, copywriting, cold email, SEO, AI SEO, paid ads, ad creative, churn prevention, pricing strategy, referral programs, and more",
       "source": "./",
       "strict": false,
       "skills": [
@@ -44,6 +44,7 @@
         "./skills/schema-markup",
         "./skills/seo-audit",
         "./skills/signup-flow-cro",
+        "./skills/site-architecture",
         "./skills/social-content"
       ]
     }