style: badges centered to flags, wider dashboard, mobile header actions

MatchCard:
- Badges (group, countdown, LIVE, BEENDET) now vertically centered
  to flag height, positioned left/right of the teams
- Removed separate topRow — all in one matchBlock flex layout

Dashboard:
- max-width increased to 800px (matches spielplan width)

Header:
- Theme toggle + admin link moved to headerActions (always visible)
- Theme toggle icon in gold color (was too dark in dark mode)
- Admin link brighter (text-secondary instead of text-muted)

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

frontend/src/App.tsx

@@ -93,6 +93,8 @@ export default function App() {
             <NavLink to="/profil" className={({ isActive }) => isActive ? styles.navLinkActive : styles.navLink}>
               Mein Profil
             </NavLink>
+          </nav>
+          <div className={styles.headerActions}>
             <NavLink to="/admin" className={styles.adminLink} title="Admin">
               <Settings size={16} />
             </NavLink>
@@ -104,7 +106,7 @@ export default function App() {
             >
               {theme === 'dark' ? <Sun size={16} /> : <Moon size={16} />}
             </button>
-          </nav>
+          </div>
         </div>
       </header>