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/pages/WishlistPage.test.jsx

@@ -0,0 +1,72 @@
+// @vitest-environment jsdom
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+import {cleanup, fireEvent, render, screen, waitFor} from '@testing-library/react';
+import {MemoryRouter, Route, Routes, useLocation} from 'react-router-dom';
+import WishlistPage from './WishlistPage.jsx';
+
+vi.mock('react-i18next', () => import('../test/i18n-mock.js'));
+
+const wishlist = {games: [
+    {appid: 1257610, name: 'Prison Architect 2', addedAt: '2026-01-01T00:00:00Z', price: '7,49€', originalPrice: '29,99€', discountPct: 75},
+    {appid: 3012600, name: 'Coming Soon', addedAt: '2025-06-01T00:00:00Z', price: null, originalPrice: null, discountPct: 0},
+]};
+
+function LoginState() {
+    return <div data-testid="login">{JSON.stringify(useLocation().state)}</div>;
+}
+
+const renderPage = () => render(
+    <MemoryRouter initialEntries={['/wishlist']}>
+        <Routes>
+            <Route path="/wishlist" element={<WishlistPage/>}/>
+            <Route path="/login" element={<LoginState/>}/>
+        </Routes>
+    </MemoryRouter>,
+);
+
+describe('WishlistPage', () => {
+    beforeEach(() => {
+        localStorage.setItem('tbp_jwt', 'token');
+        globalThis.fetch = vi.fn(async () => ({ok: true, status: 200, json: async () => wishlist}));
+    });
+
+    afterEach(() => {
+        cleanup();
+        localStorage.clear();
+    });
+
+    it('shows each game with its price, and the discount for games on sale', async () => {
+        renderPage();
+
+        expect(await screen.findByText('Prison Architect 2')).toBeTruthy();
+        expect(screen.getByText('-75%')).toBeTruthy();
+        expect(screen.getByText('7,49€')).toBeTruthy();
+        expect(screen.getByText('29,99€')).toBeTruthy();
+        expect(screen.getByText('Coming Soon')).toBeTruthy();
+        expect(screen.getByText('WISHLIST.NO_PRICE')).toBeTruthy();
+    });
+
+    it('can show only the games on sale', async () => {
+        renderPage();
+        await screen.findByText('Coming Soon');
+
+        fireEvent.click(screen.getByRole('button', {name: /WISHLIST.ONLY_ON_SALE/}));
+
+        expect(screen.queryByText('Coming Soon')).toBeNull();
+        expect(screen.getByText('Prison Architect 2')).toBeTruthy();
+    });
+
+    it('explains an empty or private wishlist', async () => {
+        fetch.mockResolvedValueOnce({ok: true, status: 200, json: async () => ({games: []})});
+        renderPage();
+
+        expect(await screen.findByText('WISHLIST.EMPTY')).toBeTruthy();
+    });
+
+    it('opens the login page on a 401', async () => {
+        fetch.mockResolvedValueOnce({ok: false, status: 401, json: async () => ({})});
+        renderPage();
+
+        await waitFor(() => expect(JSON.parse(screen.getByTestId('login').textContent).sessionExpired).toBe(true));
+    });
+});