docs(site): add Search Console verification meta, GA4 gtag, and website analytics notice

docs/osgkeyboardversion.html

@@ -3,6 +3,15 @@
 <head>
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
+  <!-- Google tag (gtag.js) -->
+  <script async src="https://www.googletagmanager.com/gtag/js?id=G-H4WM522F4C"></script>
+  <script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+
+    gtag('config', 'G-H4WM522F4C');
+  </script>
   <title>OSGKeyboard — What's New / 更新说明</title>
   <meta name="robots" content="noindex">
   <meta name="color-scheme" content="light dark">