fix(segment-wrapper): prevent Safari ITP from clearing referrer and campaign tracking params

[kikoruiz]

Summary

Fixes Safari ITP (Intelligent Tracking Prevention) issue where document.referrer and campaign tracking parameters are cleared after page load, causing loss of attribution data in analytics.

Problem

Safari ITP:

• Clears document.referrer after page load, losing external referrer information
• Strips UTM/campaign parameters from URL via redirects
• Causes first page events to have empty referrer and missing campaign data

Solution

Capture critical values at module load time before Safari ITP can clear them:

pageReferrer.js:

• INITIAL_DOCUMENT_REFERRER - captured at module load
• INITIAL_SEARCH_STRING - captured before parameter stripping
• INITIAL_URL - captured for first page event
• Direct initialization of referrerState.referrer with captured value

googleRepository.js:

• Changed retargeting medium mapping: rt: 'display' → rt: 'retargeting'

Changes

• /src/middlewares/source/pageReferrer.js - Module-load capture of referrer, search, and URL
• /src/repositories/googleRepository.js - Retargeting medium mapping fix
• /test/stubs.js - Updated test stubs for referrer state management
• /test/segmentWrapperSpec.js - Added Safari ITP protection tests, removed incorrect test

Testing

• ✅ 108 tests passing
• ✅ New tests verify referrer/search capture at module load
• ✅ Existing referrer tests updated for new initialization behavior