Add Open Graph/Twitter meta tags and Google Analytics

Social preview uses the original bb logo and the system-requirements
blurb already quoted in the footer, so a shared link matches what the
page itself says.

Claude-Session: https://claude.ai/code/session_01F6QKUwwiAxLNkYn4dv5TfW

Author: chrisns

web/index.html

@@ -4,6 +4,28 @@
 <meta charset="utf-8">
 <title>bb — ASCII art demo (WebAssembly)</title>
 <meta name="viewport" content="width=device-width, initial-scale=1">
+<meta name="description" content="&quot;This demo requires computer at least as fast as 486/33 with coprocesor. But speed of 486/66 or pentium is highly recomended (especially for hight resolution SVGA modes). This demo does not require real operating system - works even under MS-DOS. For dual monitor modes you need secondary hercules / MDA compatible card. To compile demo you need 32 or 64 bit ANSI C compiler (no it does not compile under Borland one) and libraries listed bellow. PC speaker driver eats lots of CPU so running it at computers slower than pentium is really not good idea.&quot;">
+<meta property="og:type" content="website">
+<meta property="og:url" content="https://bb.cns.me/">
+<meta property="og:site_name" content="bb">
+<meta property="og:title" content="bb — ASCII art demo (WebAssembly)">
+<meta property="og:description" content="&quot;This demo requires computer at least as fast as 486/33 with coprocesor. But speed of 486/66 or pentium is highly recomended (especially for hight resolution SVGA modes). This demo does not require real operating system - works even under MS-DOS. For dual monitor modes you need secondary hercules / MDA compatible card. To compile demo you need 32 or 64 bit ANSI C compiler (no it does not compile under Borland one) and libraries listed bellow. PC speaker driver eats lots of CPU so running it at computers slower than pentium is really not good idea.&quot;">
+<meta property="og:image" content="https://bb.cns.me/bb-logo.jpg">
+<meta property="og:image:width" content="238">
+<meta property="og:image:height" content="173">
+<meta name="twitter:card" content="summary">
+<meta name="twitter:title" content="bb — ASCII art demo (WebAssembly)">
+<meta name="twitter:description" content="&quot;This demo requires computer at least as fast as 486/33 with coprocesor. But speed of 486/66 or pentium is highly recomended (especially for hight resolution SVGA modes). This demo does not require real operating system - works even under MS-DOS. For dual monitor modes you need secondary hercules / MDA compatible card. To compile demo you need 32 or 64 bit ANSI C compiler (no it does not compile under Borland one) and libraries listed bellow. PC speaker driver eats lots of CPU so running it at computers slower than pentium is really not good idea.&quot;">
+<meta name="twitter:image" content="https://bb.cns.me/bb-logo.jpg">
+<!-- Google tag (gtag.js) -->
+<script async src="https://www.googletagmanager.com/gtag/js?id=G-HHZBLWZ5Y2"></script>
+<script>
+  window.dataLayer = window.dataLayer || [];
+  function gtag(){dataLayer.push(arguments);}
+  gtag('js', new Date());
+
+  gtag('config', 'G-HHZBLWZ5Y2');
+</script>
 <style>
   html, body {
     height: 100%;