Refactor code structure and remove redundant changes

src-old/hooks/use-mobile.tsx

@@ -0,0 +1,30 @@
+import * as React from "react";
+
+const MOBILE_BREAKPOINT = 768;
+
+export function useIsMobile(): boolean | undefined {
+  const [isMobile, setIsMobile] = React.useState<boolean | undefined>(undefined);
+
+  React.useEffect(() => {
+    // Guard against server-side rendering
+    if (typeof window === 'undefined') return;
+    
+    const mql = window.matchMedia(`(max-width: ${MOBILE_BREAKPOINT - 1}px)`);
+    
+    // Use MediaQueryList.matches instead of window.innerWidth for consistency
+    const onChange = () => {
+      setIsMobile(mql.matches);
+    };
+    
+    // Set initial value
+    setIsMobile(mql.matches);
+    
+    // Listen for changes
+    mql.addEventListener("change", onChange);
+    
+    // Cleanup listener on unmount
+    return () => mql.removeEventListener("change", onChange);
+  }, []);
+
+  return isMobile;
+}