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/PlayNextPage.jsx

@@ -23,8 +23,9 @@ const BUDGETS = [
     {key: 'LONG', maxMinutes: 2400},
     {key: 'ANY', maxMinutes: null},
 ];
-// The moods Core derives from IGDB's genres, themes and game modes; a mood leaves out games without IGDB data.
-const MOODS = ['ANY', 'STORY', 'COOP', 'CHILL', 'ACTION', 'SCARY'];
+// Core derives the moods from IGDB's genres, themes and game modes, and SPEEDRUN from speedrun.com; a mood leaves out
+// games without that data.
+const MOODS = ['ANY', 'STORY', 'COOP', 'CHILL', 'ACTION', 'SCARY', 'SPEEDRUN'];
 const PICK_COUNT = 3;
 // The backend reads only this many excludes. With a bigger backlog the oldest seen games can come back.
 const MAX_EXCLUDES = 100;
@@ -144,7 +145,9 @@ export default function PlayNextPage() {
                     ))}
                 </div>
                 {mood !== 'ANY' && (
-                    <p className="text-xs text-muted-foreground">{t('PLAY_NEXT.MOOD_HINT')}</p>
+                    <p className="text-xs text-muted-foreground">
+                        {t(mood === 'SPEEDRUN' ? 'PLAY_NEXT.MOOD_HINT_SPEEDRUN' : 'PLAY_NEXT.MOOD_HINT')}
+                    </p>
                 )}
             </div>
 
@@ -188,6 +191,8 @@ export default function PlayNextPage() {
 }
 
 const emptyKey = (budget, mood) => {
+    // With a length limit, waiting for the background check may never help.
+    if (mood === 'SPEEDRUN' && !budget.maxMinutes) return 'PLAY_NEXT.EMPTY_SPEEDRUN';
     if (mood !== 'ANY') return 'PLAY_NEXT.EMPTY_MOOD';
     return budget.maxMinutes ? 'PLAY_NEXT.EMPTY_BUDGET' : 'PLAY_NEXT.EMPTY';
 };