feat: FIFA WM 2026 unofficial logo in header (PNG)

Unofficial logo works in both dark and light mode (colored on transparent).
Official and white variants also included as alternatives.
Removed broken SVG files (Cloudflare blocked downloads).

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={theme === 'dark' ? '/assets/wm2026-logo-white.svg' : '/assets/wm2026-logo.svg'}
+              src="/assets/wm2026-logo.png"
               alt="FIFA WM 2026"
               className={styles.logoImg}
             />