perf(P6A.T2): respect prefers-reduced-motion globally + gate confetti

- Update globals.css reduced-motion block: 0.01ms → 0.001ms durations
  and add scroll-behavior: auto to suppress all transitions/animations
  when OS reduced-motion preference is active.
- Gate canvas-confetti burst in GameModal behind matchMedia check so
  the particle effect is skipped entirely for users who opt out of motion.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/desktop/src/components/GameModal.tsx

@@ -48,6 +48,14 @@ export function GameModal({ gameId, onClose }: Props) {
 
   useEffect(() => {
     if (finished && winnerIdx !== null && winnerIdx === myPlayerIdx) {
+      // Respect the OS-level reduced-motion preference.
+      if (
+        typeof window !== 'undefined' &&
+        window.matchMedia &&
+        window.matchMedia('(prefers-reduced-motion: reduce)').matches
+      ) {
+        return;
+      }
       // Two bursts from the lower corners for a celebratory feel.
       void confetti({
         particleCount: 80,

apps/desktop/src/styles/globals.css

@@ -85,9 +85,10 @@
     *,
     *::before,
     *::after {
-      animation-duration: 0.01ms !important;
+      animation-duration: 0.001ms !important;
       animation-iteration-count: 1 !important;
-      transition-duration: 0.01ms !important;
+      transition-duration: 0.001ms !important;
+      scroll-behavior: auto !important;
     }
   }
 }