Replace 'any' types in referral tracking utilities

[Mosas2000]

Description

The referral tracking utilities use any types for tracking data and Google Analytics integration, reducing type safety.

Locations

File: frontend/src/utils/referralTracking.ts
Lines: 96, 167

Impact

• Reduces type safety in referral tracking
• Makes it impossible to catch type errors at compile time
• Can lead to incorrect analytics data

Proposed Solution

Define proper interfaces for referral conversion data and Google Analytics integration.

Priority

🟡 HIGH - Type safety in analytics