fix: Sync currentTime when user selects a frame in timeline

frontend/src/components/preview/preview-player.tsx

@@ -88,6 +88,23 @@ export function PreviewPlayer() {
 
     const selectedFrame = storyboard?.frames.find((f) => f.id === selectedFrameId)
 
+    // Sync currentTime when user selects a frame (not during playback)
+    useEffect(() => {
+        if (isPlaying || !storyboard?.frames.length || !selectedFrameId) return
+
+        // Calculate start time of selected frame
+        let startTime = 0
+        for (const frame of storyboard.frames) {
+            if (frame.id === selectedFrameId) break
+            startTime += frame.duration
+        }
+
+        // Only update if different (avoid infinite loop)
+        if (Math.abs(currentTime - startTime) > 0.1) {
+            setCurrentTime(startTime)
+        }
+    }, [selectedFrameId, isPlaying])
+
     // Audio playback sync
     useEffect(() => {
         if (!audioRef.current) return