fix: add table of contents to all reference files

Per Anthropic's Agent Skills best practices, reference files over
  100 lines should include a TOC so Claude can see full scope when
  previewing with partial reads. Added ## Contents section to all
  32 reference files.

skills/email-sequence/references/copy-guidelines.md

@@ -1,5 +1,15 @@
 # Email Copy Guidelines
 
+## Contents
+- Structure
+- Formatting
+- Tone
+- Length
+- CTA Buttons vs. Links
+- Personalization (merge fields, dynamic content, triggered emails)
+- Segmentation Strategies (by behavior, by stage, by profile)
+- Testing and Optimization (what to test, how to test, metrics to track)
+
 ## Structure
 
 1. **Hook**: First line grabs attention

skills/email-sequence/references/email-types.md

@@ -2,6 +2,15 @@
 
 A comprehensive guide to lifecycle and campaign emails. Use this as an audit checklist and implementation reference.
 
+## Contents
+- Onboarding Emails (new users series, new customers series, key onboarding step reminder, new user invite)
+- Retention Emails (upgrade to paid, upgrade to higher plan, ask for review, offer support proactively, product usage report, NPS survey, referral program)
+- Billing Emails (switch to annual, failed payment recovery, cancellation survey, upcoming renewal reminder)
+- Usage Emails (daily/weekly/monthly summary, key event or milestone notifications)
+- Win-Back Emails (expired trials, cancelled customers)
+- Campaign Emails (monthly roundup/newsletter, seasonal promotions, product updates, industry news roundup, pricing update)
+- Email Audit Checklist (onboarding, retention, billing, usage, win-back, campaigns)
+
 ## Onboarding Emails
 
 ### New Users Series

skills/email-sequence/references/sequence-templates.md

@@ -2,6 +2,12 @@
 
 Detailed templates for common email sequences.
 
+## Contents
+- Welcome Sequence (Post-Signup)
+- Lead Nurture Sequence (Pre-Sale)
+- Re-Engagement Sequence
+- Onboarding Sequence (Product Users)
+
 ## Welcome Sequence (Post-Signup)
 
 **Email 1: Welcome (Immediate)**