feat: add churn-prevention skill for cancel flows, save offers, and dunning

Covers voluntary churn (exit surveys, dynamic save offers, pause/downgrade,
cancel flow UI patterns) and involuntary churn (smart retries, dunning emails,
card updaters, grace periods). Includes Churnkey-style offer-to-reason mapping,
health scoring model, proactive retention triggers, and provider-specific
dunning setup for Stripe, Chargebee, Paddle, and Recurly.

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

README.md

@@ -20,6 +20,7 @@ Skills are markdown files that give AI agents specialized knowledge and workflow
 | [ab-test-setup](skills/ab-test-setup/) | When the user wants to plan, design, or implement an A/B test or experiment. Also use when the user mentions "A/B... |
 | [ad-creative](skills/ad-creative/) | When the user wants to generate, iterate, or scale ad creative — headlines, descriptions, primary text, or full ad... |
 | [analytics-tracking](skills/analytics-tracking/) | When the user wants to set up, improve, or audit analytics tracking and measurement. Also use when the user mentions... |
+| [churn-prevention](skills/churn-prevention/) | When the user wants to reduce churn, build cancellation flows, set up save offers, recover failed payments, or implement... |
 | [cold-email](skills/cold-email/) | Write B2B cold emails and follow-up sequences that get replies. Use when the user wants to write cold outreach emails,... |
 | [competitor-alternatives](skills/competitor-alternatives/) | When the user wants to create competitor comparison or alternative pages for SEO and sales enablement. Also use when... |
 | [content-strategy](skills/content-strategy/) | When the user wants to plan a content strategy, decide what content to create, or figure out what topics to cover. Also... |
@@ -175,6 +176,9 @@ You can also invoke skills directly:
 - `analytics-tracking` - Event tracking setup
 - `ab-test-setup` - Experiment design
 
+### Retention
+- `churn-prevention` - Cancel flows, save offers, dunning, payment recovery
+
 ### Growth Engineering
 - `free-tool-strategy` - Marketing tools and calculators
 - `referral-program` - Referral and affiliate programs