feat(ops): 限制告警规则最多显示6个，超出可滚动

frontend/src/views/admin/ops/components/OpsAlertRulesCard.vue

@@ -429,10 +429,10 @@ function cancelDelete() {
       {{ t('admin.ops.alertRules.empty') }}
     </div>
 
-    <div v-else class="overflow-hidden rounded-xl border border-gray-200 dark:border-dark-700">
-      <div class="overflow-x-auto">
+    <div v-else class="max-h-[520px] overflow-hidden rounded-xl border border-gray-200 dark:border-dark-700">
+      <div class="max-h-[520px] overflow-y-auto">
         <table class="min-w-full divide-y divide-gray-200 dark:divide-dark-700">
-          <thead class="bg-gray-50 dark:bg-dark-900">
+          <thead class="sticky top-0 z-10 bg-gray-50 dark:bg-dark-900">
             <tr>
               <th class="px-4 py-3 text-left text-[11px] font-bold uppercase tracking-wider text-gray-500 dark:text-gray-400">
                 {{ t('admin.ops.alertRules.table.name') }}