fix(studio): pause all media elements in iframe on seek

When seeking via the slider or timeline scrub, explicitly pause all
<video> and <audio> elements inside the preview iframe. The GSAP
timeline pauses but iframe media elements can continue playing
independently, causing audio to keep going after a seek.

packages/studio/src/player/hooks/useTimelinePlayer.ts

@@ -407,6 +407,16 @@ export function useTimelinePlayer() {
         if (usePlayerStore.getState().isPlaying) setIsPlaying(false);
         shuttleDirectionRef.current = null;
         shuttleSpeedIndexRef.current = 0;
+        try {
+          const doc = iframeRef.current?.contentDocument;
+          if (doc) {
+            for (const el of doc.querySelectorAll("video, audio")) {
+              (el as HTMLMediaElement).pause();
+            }
+          }
+        } catch {
+          /* cross-origin */
+        }
       }
       return true;
     },