feat: the site counts anonymous visits with GoatCounter

GoatCounter: no cookies, no IP or user-agent stored, EU-hosted. count.js is
vendored into public/ so no file loads from a foreign origin — only the count
request itself leaves. The /count endpoint is documented as staying
compatible, so the copy does not go stale.

index.html

@@ -25,6 +25,10 @@
     <link rel="apple-touch-icon" href="/icon-192.png" />
     <meta name="theme-color" content="#e6e9eb" media="(prefers-color-scheme: light)" />
     <meta name="theme-color" content="#2f2f31" media="(prefers-color-scheme: dark)" />
+    <!-- Anonymous visit counting. count.js is vendored, so no file loads from a
+         foreign origin; only the count request itself leaves. -->
+    <script data-goatcounter="https://edentext.goatcounter.com/count"
+            async src="/count.js"></script>
   </head>
   <body>
     <div id="app">