Wire Google Analytics 4 (G-V8QWB45G6X) alongside Umami

Adds gtag.js to the production head so Search Console can cross-reference
GA traffic. Same gating as Umami — production builds only, never injected
on dev. Three head entries:

  1. Umami (kept) — self-hosted, DNT-aware, GDPR-light
  2. Google's gtag loader (async)
  3. Inline init: window.dataLayer + gtag('config', 'G-V8QWB45G6X')

Both analytics run side-by-side; pick one or both in the GA dashboard.
A GDPR consent banner is not added — configure IP anonymisation +
consent mode v2 in the GA property settings if you intend to serve EU
visitors without explicit cookie acceptance.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/astro.config.mjs

@@ -128,9 +128,12 @@ export default defineConfig({
 			title: 'Nibiru',
 			description:
 				'A modular MMVC PHP framework for rapid prototyping. Born among the old gods, built for modern builders.',
-			// Umami analytics — self-hosted, cookie-free, honours Do-Not-Track.
-			// No GDPR consent banner needed because no PII or cross-site state
-			// is captured. The script is only injected on production builds.
+			// Analytics — production-only.
+			//   1. Umami (self-hosted) — cookie-free, honours Do-Not-Track,
+			//      no PII captured, no GDPR banner required.
+			//   2. Google Analytics 4 (gtag.js) — added for Search Console
+			//      cross-linking + audience reach. Subject to GDPR; configure
+			//      consent / IP-anonymisation in the GA property settings.
 			head: import.meta.env.PROD
 				? [
 						{
@@ -143,6 +146,21 @@ export default defineConfig({
 								'data-exclude-search': 'true',
 							},
 						},
+						{
+							tag: 'script',
+							attrs: {
+								async: true,
+								src: 'https://www.googletagmanager.com/gtag/js?id=G-V8QWB45G6X',
+							},
+						},
+						{
+							tag: 'script',
+							content:
+								"window.dataLayer = window.dataLayer || [];\n" +
+								"function gtag(){dataLayer.push(arguments);}\n" +
+								"gtag('js', new Date());\n" +
+								"gtag('config', 'G-V8QWB45G6X');",
+						},
 				  ]
 				: [],
 			logo: {