feat(library): show playtime per platform on game detail

Hero and library card show the set total. Fall back to the
row's own minutes when the API sends no total.

src/pages/GameLibrary.test.jsx

@@ -235,6 +235,16 @@ describe('GameLibrary short games', () => {
         expect(screen.queryByText('Steam')).toBeNull();
     });
 
+    it('showsTheSetTotalPlaytimeOnTheCard_AndTheOwnMinutesWithoutATotal', async () => {
+        answer([{appid: 220, name: 'Half-Life 2', playtimeMinutes: 600, totalPlaytimeMinutes: 3600, status: 'BACKLOG'},
+            {appid: 620, name: 'Portal 2', playtimeMinutes: 1200, status: 'BACKLOG'}]);
+        renderLibrary();
+
+        expect(await screen.findByText('60h')).toBeTruthy();
+        expect(screen.getByText('20h')).toBeTruthy();
+        expect(screen.queryByText('10h')).toBeNull();
+    });
+
     it('leaves the hidden games with a status click', async () => {
         const lib = renderLibrary('/library?hidden=true');
         await waitFor(() => expect(fetch).toHaveBeenCalled());