Adds a "Measurement ID" input under admin → Site Identity. The value
is stored as identity/ga_id (existing bulk-settings endpoint, no API
change). When set, _Layout injects the GA4 gtag.js snippet into <head>
on every page (home, blog, gallery, posts). Empty value = disabled.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
soroush.asadi
82d9720e25