feat(picker): add the speedrun mood and the speedrun.com link

"What to play next" gets a Speedrun mood. The game detail links the
game's speedrun.com page when Core found one with verified runs; only
https://www.speedrun.com/ links are shown.

src/pages/GameDetail.test.jsx

@@ -35,6 +35,24 @@ afterEach(() => {
 });
 
 describe('GameDetail', () => {
+    it('links the speedrun.com page when Core found one', async () => {
+        globalThis.fetch = vi.fn(async () => ({ok: true, status: 200,
+            json: async () => ({...game, speedrunUrl: 'https://www.speedrun.com/hl2'})}));
+        renderDetail();
+
+        const link = await screen.findByRole('link', {name: /GAME_DETAIL.OPEN_IN_SPEEDRUN/});
+        expect(link.getAttribute('href')).toBe('https://www.speedrun.com/hl2');
+    });
+
+    it.each([null, 'https://www.speedrun.com.evil.example/hl2', 'https://evil.example/hl2', 42])(
+        'shows no speedrun link for %s', async (speedrunUrl) => {
+            globalThis.fetch = vi.fn(async () => ({ok: true, status: 200, json: async () => ({...game, speedrunUrl})}));
+            renderDetail();
+
+            await screen.findByText('GAME_DETAIL.OPEN_IN_STEAM');
+            expect(screen.queryByText('GAME_DETAIL.OPEN_IN_SPEEDRUN')).toBeNull();
+        });
+
     it('keeps unsaved notes in the backlog card when the hint sets the game to playing', async () => {
         renderDetail();
         const notes = await screen.findByLabelText('BACKLOG.NOTES_LABEL');