feat: WM 2026 trophy SVG without text in header

Extracted trophy graphic from unofficial logo SVG, removed
"FIFA WORLD CUP", "2026", and country names text.
Works in both dark and light mode (colored on transparent).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -78,7 +78,7 @@ export default function App() {
         <div className={styles.headerInner}>
           <div className={styles.logo}>
             <img
-              src="/assets/wm2026-logo.png"
+              src="/assets/wm2026-trophy.svg"
               alt="FIFA WM 2026"
               className={styles.logoImg}
             />