Report hanzo.chat to its own GA4 stream

hanzo.chat had no GA.  Configure G-GRQBMNDTT6 inline in the head, keyed
by host because one document serves every brand, and fetch gtag.js
after the load event so a dropped Google host cannot hold the page.
The linker keeps a visit one session across the Hanzo domains, and GPC
or DNT opts out.

index.html

@@ -21,6 +21,27 @@
         height: 100dvh;
       }
     </style>
+    <!-- GA4, each brand host to its own stream: this one document serves every
+         brand, so a host with no stream here sends nothing. The first page view
+         queues before the bundle; gtag.js is fetched after `load`, since a script
+         in the head holds the load event until its host answers. Route changes
+         are GA4's own history listener. Global Privacy Control and Do Not Track
+         opt out. -->
+    <script>
+      var tid = { 'hanzo.chat': 'G-GRQBMNDTT6' }[location.hostname];
+      if (tid && !navigator.globalPrivacyControl && navigator.doNotTrack !== '1') {
+        window.dataLayer = window.dataLayer || [];
+        function gtag(){dataLayer.push(arguments)}
+        gtag('js', new Date());
+        gtag('config', tid, { linker: { domains: [location.hostname, 'hanzo.ai', 'hanzo.id', 'pay.hanzo.ai', 'cal.hanzo.ai'] } });
+        addEventListener('load', function () {
+          var s = document.createElement('script');
+          s.async = true;
+          s.src = 'https://www.googletagmanager.com/gtag/js?id=' + tid;
+          document.head.appendChild(s);
+        }, { once: true });
+      }
+    </script>
   </head>
   <body>
     <div id="root"></div>