feat(play-next): show picks as category rows with reroll per row

Four rows: up next, because you played, longest on list, mood.
Each row rerolls alone and tracks its own loading state.
Mood change reloads only the mood row. Phones scroll each row
sideways; wider screens show 3 columns.

src/pages/PlayNextPage.language.test.jsx

@@ -20,7 +20,7 @@ describe('PlayNextPage on a language change', () => {
     beforeEach(() => {
         localStorage.setItem('tbp_session', '1');
         i18n.t = (key) => key;
-        fetchRoutes({'GET /api/library/picker': json(200, {games: [game(1)]})});
+        fetchRoutes({'GET /api/library/picker': json(200, {categories: [{source: 'RANDOM', games: [game(1)]}]})});
     });
 
     afterEach(() => {