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>

tools/integrations/composio.md

@@ -184,7 +184,7 @@ Agent uses `SALESFORCE` to read leads and `SLACK` to post messages.
 
 ## Relevant Skills
 
-- analytics-tracking (cross-platform data via Composio connectors)
-- email-sequence (ActiveCampaign, Klaviyo access)
+- analytics (cross-platform data via Composio connectors)
+- emails (ActiveCampaign, Klaviyo access)
 - paid-ads (Meta Ads, LinkedIn Ads MCP access)
-- referral-program (Shopify integration)
+- referrals (Shopify integration)