헤더 및 야드 이름 z-index 수정

frontend/components/layout/MainHeader.tsx

@@ -14,7 +14,7 @@ interface MainHeaderProps {
  */
 export function MainHeader({ user, onSidebarToggle, onProfileClick, onLogout }: MainHeaderProps) {
   return (
-    <header className="bg-background/95 sticky top-0 z-50 h-14 min-h-14 w-full flex-shrink-0 border-b backdrop-blur">
+    <header className="bg-background/95 fixed top-0 z-50 h-14 min-h-14 w-full flex-shrink-0 border-b backdrop-blur">
       <div className="flex h-full w-full items-center justify-between px-6">
         {/* Left side - Side Menu + Logo */}
         <div className="flex h-8 items-center gap-2">