docs: update ab-testing internal/claude docs

Author: wackerow

CLAUDE.md

@@ -192,6 +192,58 @@ pnpm events-import         # Import community events
 - `wagmi` - React hooks for Ethereum
 - `@rainbow-me/rainbowkit` - Wallet connection
 
+## A/B Testing
+
+### Overview
+
+The site uses a GDPR-compliant, cookie-less A/B testing system integrated with Matomo. Tests are configured entirely through the Matomo dashboard with no code changes required.
+
+### Key Features
+
+- **Matomo API Integration** - Experiments configured in Matomo dashboard
+- **Cookie-less Tracking** - Uses deterministic IP + User-Agent fingerprinting
+- **Server-side Rendering** - No layout shifts, consistent variants on first load
+- **Real-time Updates** - Change weights instantly via Matomo (no deployments)
+- **Preview Mode** - Debug panel available in development and preview environments
+- **Automatic Fallbacks** - Graceful degradation when API fails (shows original variant)
+
+### Adding a New A/B Test
+
+1. **Create experiment in Matomo dashboard**:
+   - Go to Experiments → Manage Experiments
+   - Create new experiment with desired name (e.g., "HomepageHero")
+   - Add variations with weights (original is implicit)
+   - Set status to "running"
+
+2. **Implement in component**:
+   ```tsx
+   import ABTestWrapper from "@/components/AB/TestWrapper"
+   
+   <ABTestWrapper
+     testKey="HomepageHero"  // Must match Matomo experiment name exactly
+     variants={[
+       <OriginalComponent key="original" />,
+       <NewComponent key="variant" />
+     ]}
+     fallback={<OriginalComponent />}
+   />
+   ```
+
+**No TypeScript changes required** - the system automatically fetches configuration from Matomo.
+
+### Architecture
+
+- **`/api/ab-config`** - Fetches experiment data from Matomo API
+- **`src/lib/ab-testing/`** - Core logic for assignment and tracking
+- **`src/components/AB/`** - React components for testing and debugging
+
+### Environment Variables
+
+Required for Matomo integration:
+- `NEXT_PUBLIC_MATOMO_URL` - Matomo instance URL
+- `NEXT_PUBLIC_MATOMO_SITE_ID` - Site ID in Matomo
+- `MATOMO_API_TOKEN` - API token with experiments access
+
 ## Deployment
 
 - **Platform**: Netlify (config in `netlify.toml`)