Remove subtitle from header navigation

src/components/HeaderOpen.vue

@@ -2,14 +2,9 @@
   <header class="arena-header">
     <div class="bar">
       <!-- Title (left) -->
-      <div class="title-section">
-        <button class="arena-title" aria-label="Agent Market Arena" @click="navigateTo('/')">
-          Agent Market Arena
-        </button>
-        <p class="arena-subtitle">
-          A real-time, ever-evolving platform for continuous competition among AI trading agents.
-        </p>
-      </div>
+      <button class="arena-title" aria-label="Agent Market Arena" @click="navigateTo('/')">
+        Agent Market Arena
+      </button>
 
       <!-- Tabs (right) -->
       <nav class="menu" aria-label="Primary">
@@ -81,13 +76,6 @@ export default {
   gap: 16px;
 }
 
-/* Title section (left) */
-.title-section{
-  display: flex;
-  flex-direction: column;
-  gap: 4px;
-}
-
 /* Title with AMA gradient text */
 .arena-title{
   all: unset;
@@ -101,17 +89,6 @@ export default {
   color: transparent;
 }
 
-/* Subtitle */
-.arena-subtitle{
-  margin: 0;
-  font-size: 13px;
-  font-weight: 500;
-  color: #6b7280;
-  letter-spacing: 0.01em;
-  line-height: 1.4;
-  max-width: 450px;
-}
-
 /* Tabs (right) */
 .menu{
   display: flex; gap: 28px; align-items: center; flex-wrap: wrap;
@@ -154,9 +131,7 @@ export default {
 /* responsive */
 @media (max-width: 720px){
   .bar{ flex-direction: column; align-items: stretch; }
-  .title-section{ align-items: center; text-align: center; }
-  .arena-title{ font-size: 22px; }
-  .arena-subtitle{ font-size: 12px; max-width: 100%; }
+  .arena-title{ text-align: center; font-size: 22px; }
   .menu{ justify-content: center; gap: 18px; }
   .menu-item{ font-size: 18px; }
 }