feat: skip countdown for train mode (sprint)

Train mode now starts immediately when clicking "Start Your Race!" button,
bypassing the 3-2-1-GO countdown. Other game modes (practice, survival) still
show the countdown as expected.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/games/complement-race/components/GameControls.tsx

@@ -23,7 +23,13 @@ export function GameControls() {
   const handleStartRace = () => {
     // Update URL to match selected game style when starting
     router.push(`/games/complement-race/${state.style}`)
-    dispatch({ type: 'START_COUNTDOWN' })
+
+    // Train mode (sprint) doesn't need countdown - start immediately
+    if (state.style === 'sprint') {
+      dispatch({ type: 'BEGIN_GAME' })
+    } else {
+      dispatch({ type: 'START_COUNTDOWN' })
+    }
   }
 
   return (