Add gray circle background to pause button for better visibility

frontend/src/assets/pause.tsx

@@ -6,14 +6,18 @@ function PauseIcon() {
       xmlns="http://www.w3.org/2000/svg"
       fill="none"
       viewBox="0 0 24 24"
-      strokeWidth={1.5}
-      stroke="currentColor"
-      className="w-5 h-5"
+      className="w-5 h-5 relative"
     >
+      {/* Gray circle background */}
+      <circle cx="12" cy="12" r="10" fill="#E5E7EB" />
+      
+      {/* Pause icon lines */}
       <path
         strokeLinecap="round"
         strokeLinejoin="round"
         d="M15.75 5.25v13.5m-7.5-13.5v13.5"
+        strokeWidth={1.5}
+        stroke="currentColor"
       />
     </svg>
   );