fix(color): eliminate redundant dark: accent modifiers (R-8.29), resolve A-1/A-2/A-9 contrast issues, and implement C11-9 quality gate

refer_landing_page/app/not-found.tsx

@@ -5,7 +5,7 @@ export default function NotFound() {
   return (
     <div className="container-content py-20 sm:py-32 flex flex-col items-center justify-center text-center min-h-[60vh]">
       <div className="border border-line bg-paper p-8 sm:p-12 rounded-lg max-w-xl w-full space-y-6 shadow-sm">
-        <div className="inline-block px-3 py-1 bg-vermillion/10 text-vermillion font-mono text-xs font-bold rounded tracking-widest uppercase">
+        <div className="inline-block px-3 py-1 bg-vermillion/10 text-vermillion-dark font-mono text-xs font-bold rounded tracking-widest uppercase">
           404 Error
         </div>
         <h1 className="font-serif text-3xl sm:text-4xl font-normal text-ink leading-tight">
@@ -19,7 +19,7 @@ export default function NotFound() {
         <div className="pt-4">
           <Link
             href="/"
-            className="inline-flex items-center justify-center px-6 py-3 border border-ink bg-ink text-ivory hover:bg-vermillion hover:border-vermillion transition-colors duration-200 text-sm font-medium rounded-md"
+            className="inline-flex items-center justify-center px-6 py-3 border border-ink bg-ink text-ivory hover:bg-vermillion-dark hover:border-vermillion-dark transition-colors duration-200 text-sm font-medium rounded-md"
           >
             메인 페이지로 돌아가기
           </Link>