feat(points): balance, history and shop page

Add /points page with wallet balance, shop grouped by slot and ledger
history with game names. The wallet loads once in PreferencesContext after
login, so the header shows a balance chip and the link. Premium accents
gold and teal override the free accent while equipped. German and English.

src/App.test.jsx

@@ -29,6 +29,7 @@ describe('App', () => {
         const library = () => (expired ? json(401, {}) : json(200, page));
         fetchRoutes({
             'GET /api/users/me': json(200, {settings: {}}),
+            'GET /api/rewards/wallet': json(200, {balance: 0, catalog: [], owned: [], equipped: {}, history: []}),
             'GET /api/library/games': library,
             'GET /api/library/games-count': json(200, {hasSteamId: true}),
             'GET /api/library/steam-profile': json(200, null),