2. Add `lib/utils/analytics.ts` event tracking

[DeFiVC]

What: Add analytics event tracking utilities for user actions.

Why: Understanding user behavior requires tracking events (enrollment, quiz completion, reward claim). A utility module centralizes tracking.

Scope: Add functions for: trackEvent, trackPageView, trackError. Support multiple analytics providers (Google Analytics, Mixpanel).

Acceptance criteria:

• Events are tracked
• Page views are tracked
• Errors are tracked
• Multiple providers are supported

Technical context: src/lib/utils/analytics.ts — analytics utils. src/app/layout.tsx — root layout.

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