feat: ship a web app manifest and home-screen icons

Adding the app to a phone home screen produced a blank tile: index.html
linked only an SVG favicon, and Safari ignores SVG for apple-touch-icon,
substituting a screenshot of the page. There was no manifest at all, so
Android had nothing to install against either.

Generate the rasters from public/logo.svg with sharp, which the repo
already carries. The output is committed so a plain `vite build` needs no
image toolchain; re-run scripts/generate-icons.mjs after changing the
logo. The logo's viewBox is wider than it is tall, so each icon centres
the mark on a square #0a0a0f canvas rather than stretching it, inset to
78% normally and 54% for the maskable variant to survive Android's
circular crop.

The SVG favicon stays as the browser tab icon.

index.html

@@ -5,6 +5,16 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0" />
   <title>God's Eye View</title>
   <link rel="icon" type="image/svg+xml" href="/logo.svg" />
+  <!-- Raster fallbacks: Safari ignores an SVG apple-touch-icon and falls back to a
+       screenshot of the page, so an installed app needs a real PNG. Regenerate
+       these from the logo with `node scripts/generate-icons.mjs`. -->
+  <link rel="icon" type="image/png" sizes="32x32" href="/icons/icon-32.png" />
+  <link rel="apple-touch-icon" sizes="180x180" href="/icons/icon-180.png" />
+  <link rel="manifest" href="/manifest.webmanifest" />
+  <meta name="theme-color" content="#0a0a0f" />
+  <meta name="apple-mobile-web-app-capable" content="yes" />
+  <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent" />
+  <meta name="apple-mobile-web-app-title" content="God's Eye" />
   <link rel="stylesheet" href="/style.css" />
   <link rel="preconnect" href="https://fonts.googleapis.com" />
   <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />