Add GA4 ↔ Search Console link as done item on AI visibility scoreboard

What was done

• Added ga4-gsc-link to Phase 6 — Measurement in items.json, positioned right after the search-console monitoring item.
• Title enumerates the five reports the link surfaces in GA4: Organic Google Search Traffic, Search Queries, Landing Pages, Clicks / Impressions / CTR, Search Console acquisition reports.
• Status: done, completedAt: 2026-05-13.

Why

Ryan completed the GA4 ↔ Search Console integration and asked to record it on the public scoreboard.

Files affected

• src/content/seo-plan/items.json