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/analytics-tracking/references/event-library.md

@@ -2,6 +2,15 @@
 
 Comprehensive list of events to track by business type and context.
 
+## Contents
+- Marketing Site Events (navigation & engagement, CTA & form interactions, conversion events)
+- Product/App Events (onboarding, core usage, errors & support)
+- Monetization Events (pricing & checkout, subscription management)
+- E-commerce Events (browsing, cart, checkout, post-purchase)
+- B2B / SaaS Specific Events (team & collaboration, integration events, account events)
+- Event Properties (Parameters)
+- Funnel Event Sequences
+
 ## Marketing Site Events
 
 ### Navigation & Engagement

skills/analytics-tracking/references/ga4-implementation.md

@@ -2,6 +2,16 @@
 
 Detailed implementation guide for Google Analytics 4.
 
+## Contents
+- Configuration (data streams, enhanced measurement events, recommended events)
+- Custom Events (gtag.js implementation, Google Tag Manager)
+- Conversions Setup (creating conversions, conversion values)
+- Custom Dimensions and Metrics (when to use, setup steps, examples)
+- Audiences (creating audiences, audience examples)
+- Debugging (DebugView, real-time reports, common issues)
+- Data Quality (filters, cross-domain tracking, session settings)
+- Integration with Google Ads (linking, audience export)
+
 ## Configuration
 
 ### Data Streams

skills/analytics-tracking/references/gtm-implementation.md

@@ -2,6 +2,16 @@
 
 Detailed guide for implementing tracking via Google Tag Manager.
 
+## Contents
+- Container Structure (tags, triggers, variables)
+- Naming Conventions
+- Data Layer Patterns
+- Common Tag Configurations (GA4 configuration tag, GA4 event tag, Facebook pixel)
+- Preview and Debug
+- Workspaces and Versioning
+- Consent Management
+- Advanced Patterns (tag sequencing, exception handling, custom JavaScript variables)
+
 ## Container Structure
 
 ### Tags