feat: 搜索按钮移到顶部header，和新建按钮并列

www/style.css

@@ -66,14 +66,13 @@ body {
   font-weight: 600;
 }
 
-.list-content {
-  flex: 1;
-  padding: 16px;
-  overflow-y: auto;
+.header-actions {
+  display: flex;
+  align-items: center;
+  gap: 8px;
 }
 
-/* Header 中的新建对话按钮 - 美化版 */
-.new-chat-btn-header {
+.header-btn {
   display: flex;
   align-items: center;
   justify-content: center;
@@ -90,7 +89,7 @@ body {
   overflow: hidden;
 }
 
-.new-chat-btn-header::before {
+.header-btn::before {
   content: '';
   position: absolute;
   inset: 0;
@@ -99,25 +98,31 @@ body {
   transition: opacity 0.25s;
 }
 
-.new-chat-btn-header:hover {
+.header-btn:hover {
   transform: scale(1.08);
   box-shadow: 0 4px 16px rgba(102,126,234,0.4), 0 2px 8px rgba(0,0,0,0.2);
   color: #5a67d8;
 }
 
-.new-chat-btn-header:hover::before {
+.header-btn:hover::before {
   opacity: 1;
 }
 
-.new-chat-btn-header:active {
+.header-btn:active {
   transform: scale(0.95);
   box-shadow: 0 1px 4px rgba(0,0,0,0.2);
 }
 
-.new-chat-btn-header svg {
+.header-btn svg {
   filter: drop-shadow(0 1px 2px rgba(102,126,234,0.3));
 }
 
+.list-content {
+  flex: 1;
+  padding: 16px;
+  overflow-y: auto;
+}
+
 /* 原样式保留（备用） */
 .new-chat-btn {
   display: flex;