fix: accuracy display, Spiele nav icon, light mode card polish

- Trefferquote: accuracy already displayed correctly as raw value (no fix needed, was already `{stats.accuracy}%`)
- BottomNav: replace ⚽ emoji with Lucide Swords icon for Spiele tab (emoji rendered as gear on some systems); remove unused .emojiIcon CSS class
- Light mode: stronger card shadows (0 4px 20px + 0 1px 4px) and brighter card shine (0.85)

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

frontend/src/components/BottomNav.tsx

@@ -1,5 +1,5 @@
 import { NavLink } from 'react-router-dom';
-import { Home, Trophy, User } from 'lucide-react';
+import { Home, Trophy, User, Swords } from 'lucide-react';
 import styles from './BottomNav.module.css';
 
 export default function BottomNav() {
@@ -13,7 +13,7 @@ export default function BottomNav() {
         <span>Home</span>
       </NavLink>
       <NavLink to="/spiele" className={linkClass}>
-        <span className={styles.emojiIcon}>⚽</span>
+        <Swords size={20} />
         <span>Spiele</span>
       </NavLink>
       <NavLink to="/rangliste" className={linkClass}>