feat: 监控告警体系统一重构 + 自动化任务调度引擎 + 监控大屏拆分

告警中心
- 新增统一告警(alert_unified)、监控告警规则(monitor_alert_rule)、指标目录(alert_metric_catalog)
- 通知策略与消息分发(alert_notify_policy/dispatch/message)、静默规则
- 告警引擎按阈值/SNMP 拆分(alert_engine_monitor/snmp)

监控采集
- SNMP 常量/模板与历史指标(snmp templates/constants、snmp_metrics_history、snmp_collect)
- 中间件监控 Redis 采集与种子(middleware_monitor_redis/seed)
- 站点探测 pkg(siteprobe) + 站点视图(site_view)

自动化任务
- cron 调度器(cronscheduler)、脚本运行器(scriptrunner)、系统任务(systask)及运行记录(cron_job_run、system_task)

审计与凭证
- 审计设置(audit_setting) + 历史清理(auditcleaner)

前端
- 监控页面(host/middleware/site/snmp)拆分为子模块并大屏化
- 告警中心多 Tab(规则/指标目录/通知策略/静默)、任务管理组件重构、Agent CLI Markdown 渲染
- 移除旧脚本卡片/详情/日志组件，统一为 ScriptTable/ScriptCodeEditor/TerminalOutput

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/pages/monitor/shared/ChartExpandShell.tsx

@@ -0,0 +1,60 @@
+// 监控图表放大壳 — 复用主机监控 ChartToolbar + 宽屏弹框 // Logan.Li
+import { useState, type ReactNode } from 'react';
+import {
+  Dialog, DialogContent, DialogDescription, DialogHeader, DialogTitle,
+} from '@/components/ui/dialog';
+import { ChartToolbar } from '../host-monitor/ChartToolbar';
+
+interface Props {
+  title: string;
+  icon?: ReactNode;
+  /** 紧凑视图高度 */
+  compactHeight?: number;
+  /** 弹框内图表高度 */
+  expandedHeight?: number;
+  /** 无数据时不显示放大按钮 */
+  empty?: boolean;
+  className?: string;
+  children: (height: number) => ReactNode;
+}
+
+export function ChartExpandShell({
+  title,
+  icon,
+  compactHeight = 180,
+  expandedHeight = 420,
+  empty = false,
+  className = 'rounded-lg bg-[var(--dg-bg-tertiary)] p-3',
+  children,
+}: Props) {
+  const [expanded, setExpanded] = useState(false);
+
+  return (
+    <>
+      <div className={className}>
+        <div className="flex items-center justify-between gap-2 mb-2">
+          <div className="flex items-center gap-2 min-w-0">
+            {icon}
+            <span className="text-xs text-[var(--dg-text-muted)] truncate">{title}</span>
+          </div>
+          {!empty && <ChartToolbar onExpand={() => setExpanded(true)} />}
+        </div>
+        {empty ? (
+          <p className="text-xs text-center py-10 text-[var(--dg-text-muted)]">暂无数据</p>
+        ) : (
+          children(compactHeight)
+        )}
+      </div>
+
+      <Dialog open={expanded} onOpenChange={setExpanded}>
+        <DialogContent className="sm:max-w-4xl max-h-[90vh] overflow-y-auto bg-[var(--dg-bg-secondary)] border-[var(--dg-border)]">
+          <DialogHeader>
+            <DialogTitle className="text-base">{title}</DialogTitle>
+            <DialogDescription className="text-[var(--dg-text-muted)]">放大查看监控趋势与指标细节</DialogDescription>
+          </DialogHeader>
+          <div className="pt-2">{children(expandedHeight)}</div>
+        </DialogContent>
+      </Dialog>
+    </>
+  );
+}