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/groups/page.tsx

@@ -57,7 +57,7 @@ export default function GroupsPage() {
           })
           const letter = groupName.replace('Group ', '')
           return (
-            <div key={groupName} className="rounded-2xl overflow-hidden" style={{ background: '#0a1810', border: '1px solid rgba(34,197,94,0.15)' }}>
+            <div key={groupName} className="glass-card">
               <div className="px-4 py-3 border-b" style={{
                 background: 'linear-gradient(90deg,rgba(34,197,94,0.12) 0%,rgba(34,197,94,0.04) 100%)',
                 borderColor: 'rgba(34,197,94,0.1)',