feat(seo): apply full favicon set with sharp SVG icon

index.html

@@ -12,8 +12,15 @@
     />
     <title>Cave Survey Viewer</title>
     <meta name="google-site-verification" content="yhJBw46UtDk7-YZn_gDqYoYJpHEHPOMHRE065-Nohf4" />
+    <!-- Favicons: SVG first so capable browsers render a sharp, scalable icon;
+         PNG/ICO fallbacks for older browsers and platform-specific surfaces. -->
+    <link rel="icon" href="/favicon.svg" type="image/svg+xml" />
+    <link rel="icon" href="/favicon.ico" sizes="any" />
+    <link rel="icon" type="image/png" sizes="48x48" href="/favicon-48x48.png" />
     <link rel="icon" type="image/png" sizes="96x96" href="/favicon-96x96.png" />
-    <link rel="icon" type="image/png" href="/favicon.png" />
+    <link rel="apple-touch-icon" sizes="180x180" href="/apple-touch-icon.png" />
+    <link rel="manifest" href="/site.webmanifest" />
+    <meta name="theme-color" content="#121a28" />
     <meta name="application-name" content="Cave Survey Viewer" />
     <meta
       name="description"

public/site.webmanifest

@@ -0,0 +1,13 @@
+{
+  "name": "Cave Survey Viewer",
+  "short_name": "CaveViewer",
+  "description": "A web-native 3D viewer for cave survey data. Runs entirely in your browser.",
+  "icons": [
+    { "src": "/android-chrome-192x192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/android-chrome-512x512.png", "sizes": "512x512", "type": "image/png" }
+  ],
+  "theme_color": "#121a28",
+  "background_color": "#121a28",
+  "display": "standalone",
+  "start_url": "/"
+}