feat: add football net background pattern and glass card styling

Diagonal ±45° goal-net texture on body background. All card surfaces
converted from opaque #0a1810 to glass-card (backdrop-blur + semi-transparent
rgba) or glass-card-hero (gradient rgba) so the net pattern shows through.
Covers all pages: home, groups, history, search, stats, teams, tournaments,
players, match cards, and 404.

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

app/not-found.tsx

@@ -7,11 +7,7 @@ export default function NotFound() {
   return (
     <div className="max-w-[1200px] mx-auto px-7 py-20 flex flex-col items-center text-center">
       <div
-        className="pitch-grid rounded-2xl px-12 py-16 w-full max-w-lg"
-        style={{
-          background: 'linear-gradient(145deg,#0a1a0e 0%,#0d2416 100%)',
-          border: '1px solid rgba(34,197,94,0.2)',
-        }}
+        className="pitch-grid glass-card-hero rounded-2xl px-12 py-16 w-full max-w-lg"
       >
         <div className="font-['Bebas_Neue'] text-[120px] text-[#22c55e] leading-none">
           404