feat: add proper favicon, apple-touch-icon, webmanifest and PWA icons

Generate PNGs from the trophy SVG (dark #040d08 background, centred):
- favicon.svg       — primary, all modern browsers
- favicon-32x32.png — 32×32 fallback for older browsers
- apple-touch-icon.png — 180×180 for iOS home screen
- icon-192x192.png / icon-512x512.png — webmanifest / PWA

app/manifest.ts provides /manifest.webmanifest via Next.js file convention.
layout.tsx metadata wires up all icon sizes via the icons API.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/manifest.ts

@@ -0,0 +1,17 @@
+import type { MetadataRoute } from 'next'
+
+export default function manifest(): MetadataRoute.Manifest {
+  return {
+    name: 'World Cup',
+    short_name: 'World Cup',
+    description: 'Comprehensive World Cup statistics from 1930 to 2026',
+    start_url: '/',
+    display: 'standalone',
+    background_color: '#040d08',
+    theme_color: '#040d08',
+    icons: [
+      { src: '/icon-192x192.png', sizes: '192x192', type: 'image/png' },
+      { src: '/icon-512x512.png', sizes: '512x512', type: 'image/png' },
+    ],
+  }
+}