style: apply Primary Color (#4E77FF) to AppHeader active tabs and Hero Orchestration highlights

refer_landing_page/app/page.tsx

@@ -63,7 +63,7 @@ export default function HomePage() {
       {/* Hero Section */}
       <section className="relative">
         <div className="mb-4">
-          <span className="font-mono text-xs tracking-widest uppercase text-vermillion font-bold">
+          <span className="font-mono text-xs tracking-widest uppercase text-cobalt-dark dark:text-cobalt font-bold">
             Kyungpook National University · AI Agent Networking Lab (ANL)
           </span>
         </div>
@@ -72,7 +72,7 @@ export default function HomePage() {
           <div className="lg:col-span-7 space-y-6 lg:pt-4">
             <h1 className="font-serif text-4xl sm:text-5xl lg:text-6xl font-normal text-ink leading-tight">
               Multi-Agent <br />
-              <span className="italic font-serif text-vermillion">Orchestration</span>
+              <span className="italic font-serif text-cobalt-dark dark:text-cobalt">Orchestration</span>
             </h1>
             <p className="text-ink-mute text-base sm:text-lg leading-relaxed max-w-2xl">
               AI 에이전트 네트워크 연구실(ANL)은 멀티 AI 에이전트 오케스트레이션을 위해 서로 소통하고 협력하는 에이전트 네트워킹 기술과 표준 프레임워크 기술을 연구합니다.

refer_landing_page/components/Header.tsx

@@ -66,8 +66,8 @@ export default function Header() {
                   aria-current={active ? "page" : undefined}
                   className={`group relative flex items-baseline gap-1.5 text-[0.78rem] font-semibold uppercase tracking-[0.18em] transition-all px-3 py-1.5 rounded-md ${
                     active
-                      ? "bg-vermillion text-white dark:text-ivory shadow-sm font-bold"
+                      ? "bg-cobalt-dark text-white dark:text-ivory shadow-sm font-bold"
-                      : "text-ink hover:text-vermillion hover:bg-paper/60"
+                      : "text-ink hover:text-cobalt-dark dark:hover:text-cobalt hover:bg-paper/60"
                   }`}
                 >
                   <span
@@ -126,7 +126,7 @@ export default function Header() {
                     aria-current={active ? "page" : undefined}
                     className={`flex items-baseline justify-between px-4 py-3.5 transition-colors rounded-md my-1 ${
                       active
-                        ? "bg-vermillion text-white dark:text-ivory font-bold shadow-sm"
+                        ? "bg-cobalt-dark text-white dark:text-ivory font-bold shadow-sm"
                         : "text-ink hover:bg-paper/60"
                     }`}
                   >