feat(library): Steam wishlist tab with prices and discounts

The library page gets a Bibliothek | Wunschliste tab bar. The wishlist shows
the current store price, the discount and can show only games on sale.

src/components/AppHeader.jsx

@@ -1,4 +1,4 @@
-import {Link, NavLink} from 'react-router-dom';
+import {Link, NavLink, useLocation} from 'react-router-dom';
 import {useTranslation} from 'react-i18next';
 import {Gamepad2, Languages, LayoutDashboard, Library, LogOut, Moon, Settings, Sun, UserRound} from 'lucide-react';
 
@@ -15,10 +15,11 @@ import {cn} from '@/lib/utils';
 
 const NAV_ITEMS = [
     {to: '/dashboard', labelKey: 'NAV.DASHBOARD', Icon: LayoutDashboard},
-    {to: '/library', labelKey: 'NAV.LIBRARY', Icon: Library},
+    // The wishlist is a tab of the library.
+    {to: '/library', labelKey: 'NAV.LIBRARY', Icon: Library, alsoActiveOn: ['/wishlist']},
 ];
 
-const navLinkClass = ({isActive}) => cn(
+const navLinkClass = (isActive) => cn(
     'flex items-center gap-2 rounded-lg px-3 py-2 text-sm font-medium transition-colors',
     isActive
         ? 'bg-accent text-accent-foreground'
@@ -28,6 +29,7 @@ const navLinkClass = ({isActive}) => cn(
 export default function AppHeader({isAuthenticated, onLogout}) {
     const {t, i18n} = useTranslation();
     const {isDarkMode, setDarkMode, setLanguage} = usePreferences();
+    const {pathname} = useLocation();
 
     const toggleLanguage = () => setLanguage(i18n.language === 'de' ? 'en' : 'de');
     const toggleTheme = () => setDarkMode(!isDarkMode);
@@ -45,8 +47,9 @@ export default function AppHeader({isAuthenticated, onLogout}) {
 
                 {isAuthenticated && (
                     <nav className="flex items-center gap-1">
-                        {NAV_ITEMS.map(({to, labelKey, Icon}) => (
-                            <NavLink key={to} to={to} className={navLinkClass} title={t(labelKey)}>
+                        {NAV_ITEMS.map(({to, labelKey, Icon, alsoActiveOn = []}) => (
+                            <NavLink key={to} to={to} title={t(labelKey)}
+                                     className={({isActive}) => navLinkClass(isActive || alsoActiveOn.includes(pathname))}>
                                 <Icon className="size-4"/>
                                 <span className="hidden sm:inline">{t(labelKey)}</span>
                             </NavLink>