Add favicon

Link /assets/favicon.ico from every page and serve /favicon.ico without
requiring the access key (browsers request it on their own).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

public/table.html

@@ -6,6 +6,7 @@
   <meta name="theme-color" content="#24493b">
   <meta name="robots" content="noindex, nofollow">
   <title>テーブル - Hold'em Night</title>
+  <link rel="icon" href="/assets/favicon.ico">
   <link rel="stylesheet" href="/assets/style.css">
 </head>
 <body class="table-page">