[frontend]: Refactor into separate components

frontend/src/components/LoadingOverlay.jsx

@@ -0,0 +1,15 @@
+import React from "react";
+
+const LoadingOverlay = () => (
+    <div style={{
+        position: "absolute", top: 0, left: 0, width: "100%", height: "100%",
+        background: "rgba(0, 0, 0, 0.5)", display: "flex",
+        alignItems: "center", justifyContent: "center",
+        color: "white", fontSize: "20px", fontWeight: "bold",
+        zIndex: 1000
+    }}>
+        Loading data...
+    </div>
+);
+
+export default LoadingOverlay;