refactor(shadow): introduce shadow-card utility and extend tailwind-merge

app/(order)/chat/[id]/page.tsx

@@ -62,7 +62,7 @@ export default function ChatDetailPage({ params }: { params: Promise<{ id: strin
 
   return (
     <div className="container mx-auto max-w-3xl px-4 py-8 h-[calc(100vh-3.5rem)] flex flex-col">
-      <Card className="flex-1 flex flex-col overflow-hidden hover:shadow-[var(--shadow-card)]">
+      <Card className="flex-1 flex flex-col overflow-hidden hover:shadow-card-hover">
         <div className="border-b px-4 py-3 flex items-center gap-3 bg-muted/30">
           <Link href="/chat" className="text-muted-foreground hover:text-foreground">
             <ArrowLeft className="h-5 w-5" />

app/(order)/chat/page.tsx

@@ -58,7 +58,7 @@ export default function ChatListPage() {
         })}
 
         {sessions.length === 0 && (
-          <Card className="hover:shadow-[var(--shadow-card)]">
+          <Card className="hover:shadow-card-hover">
             <CardContent className="py-8 text-center text-sm text-muted-foreground">
               <MessageSquare className="h-12 w-12 mx-auto mb-2 opacity-50" />
               暂无消息