feat: rename 15 skills for shorter, cleaner names

Renames:
- ab-test-setup → ab-testing
- analytics-tracking → analytics
- competitor-alternatives → competitors
- email-sequence → emails
- free-tool-strategy → free-tools
- launch-strategy → launch
- onboarding-cro → onboarding
- paywall-upgrade-cro → paywalls
- popup-cro → popups
- pricing-strategy → pricing
- product-marketing-context → product-marketing
- referral-program → referrals
- schema-markup → schema
- signup-flow-cro → signup
- social-content → social

Updates all cross-references in skills, references, tools,
marketplace.json, README, AGENTS.md, and CONTRIBUTING.md.

BREAKING: Users with installed skills will need to reinstall.

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

.claude-plugin/marketplace.json

@@ -16,41 +16,42 @@
       "source": "./",
       "strict": false,
       "skills": [
-        "./skills/ab-test-setup",
+        "./skills/ab-testing",
         "./skills/ad-creative",
         "./skills/ai-seo",
+        "./skills/analytics",
         "./skills/aso-audit",
-        "./skills/analytics-tracking",
         "./skills/churn-prevention",
         "./skills/cold-email",
-        "./skills/competitor-alternatives",
+        "./skills/community-marketing",
+        "./skills/competitors",
         "./skills/content-strategy",
         "./skills/copy-editing",
         "./skills/copywriting",
         "./skills/customer-research",
-        "./skills/email-sequence",
+        "./skills/emails",
         "./skills/form-cro",
-        "./skills/free-tool-strategy",
-        "./skills/launch-strategy",
+        "./skills/free-tools",
+        "./skills/launch",
         "./skills/lead-magnets",
         "./skills/marketing-ideas",
         "./skills/marketing-psychology",
-        "./skills/onboarding-cro",
+        "./skills/onboarding",
         "./skills/page-cro",
         "./skills/paid-ads",
-        "./skills/paywall-upgrade-cro",
-        "./skills/popup-cro",
-        "./skills/pricing-strategy",
-        "./skills/product-marketing-context",
+        "./skills/paywalls",
+        "./skills/popups",
+        "./skills/pricing",
+        "./skills/product-marketing",
         "./skills/programmatic-seo",
-        "./skills/referral-program",
+        "./skills/referrals",
         "./skills/revops",
         "./skills/sales-enablement",
-        "./skills/schema-markup",
+        "./skills/schema",
         "./skills/seo-audit",
-        "./skills/signup-flow-cro",
+        "./skills/signup",
         "./skills/site-architecture",
-        "./skills/social-content"
+        "./skills/social"
       ]
     }
   ]