feat: add aria-label attributes to various components for improved accessibility

src/components/header/ButtonGroup.js

@@ -131,6 +131,7 @@ class ButtonGroup extends Component {
         <IconButton 
           color="inherit" 
           onClick={this.toggleCart}
+          aria-label="Warenkorb öffnen"
           sx={{ ml: 1 }}
         >
           <Badge badgeContent={this.state.badgeNumber} color="error">
@@ -156,6 +157,7 @@ class ButtonGroup extends Component {
               <IconButton 
                 onClick={this.toggleCart} 
                 size="small"
+                aria-label="Warenkorb schließen"
                 sx={{ 
                   bgcolor: 'primary.main',
                   color: 'primary.contrastText',