Add installable PWA shell with safe updates and offline status

web/index.html

@@ -6,6 +6,9 @@
     <meta name="theme-color" content="#ffffff" media="(prefers-color-scheme: light)" />
     <meta name="theme-color" content="#1a1a1a" media="(prefers-color-scheme: dark)" />
     <title>RawMark</title>
+    <link rel="manifest" href="/manifest.webmanifest" />
+    <link rel="icon" href="/icon.svg" type="image/svg+xml" />
+    <link rel="apple-touch-icon" href="/icons/apple-touch-icon.png" />
   </head>
   <body>
     <div id="app"></div>