feat: 审核规则模版+设置页面整合+去掉角色切换demo

后端:
- AuditRule 新增 value 字段, rule_type 扩展 DDL/DML
- MySQL/PG/Redis 预设规则种子接口 POST /audit-rules/seed/{db_type}
- 公告管理 CRUD (announcements)
- 消息推送 CRUD+测试 (notifications: 钉钉/飞书/邮件)
- LDAP 配置 CRUD+测试连接 (ldap-config)
- 164 tests passing (+31 新增)

前端:
- AuditRulesPage 重写: DB类型Tab+DDL/DML分组+参数编辑
- SettingsPage: 系统设置主页(审核规则/公告/推送/LDAP)
- NotificationPage: 钉钉/飞书/SMTP配置
- LdapConfigPage: LDAP设置+测试连接
- AnnouncementPage: 公告Markdown编辑
- 去掉左下角角色切换demo
- 侧边栏合并为: 系统设置(含审核规则+公告+推送+LDAP)

frontend/src/pages/SettingsPage.tsx

@@ -0,0 +1,53 @@
+import { useState } from 'react';
+import AnnouncementPage from './AnnouncementPage';
+import NotificationPage from './NotificationPage';
+import LdapConfigPage from './LdapConfigPage';
+import AuditRulesPage from './AuditRulesPage';
+
+const tabs = [
+  { id: 'rules', label: '审核规则', icon: '🛡️' },
+  { id: 'announcement', label: '公告管理', icon: '📢' },
+  { id: 'notification', label: '消息推送', icon: '🔔' },
+  { id: 'ldap', label: 'LDAP', icon: '🔐' },
+] as const;
+
+type TabId = typeof tabs[number]['id'];
+
+export default function SettingsPage() {
+  const [activeTab, setActiveTab] = useState<TabId>('rules');
+
+  return (
+    <div className="space-y-5">
+      <div>
+        <h1 className="text-xl font-semibold">系统设置</h1>
+        <p className="text-sm text-[var(--dg-text-muted)] mt-1">管理平台配置、审核规则、消息推送和 LDAP 认证</p>
+      </div>
+
+      {/* Tab 导航 */}
+      <div className="flex gap-1 p-1 bg-[var(--dg-bg-tertiary)] rounded-xl w-fit">
+        {tabs.map(tab => (
+          <button
+            key={tab.id}
+            onClick={() => setActiveTab(tab.id)}
+            className={`flex items-center gap-2 px-4 py-2 rounded-lg text-sm font-medium transition-all ${
+              activeTab === tab.id
+                ? 'bg-[var(--dg-bg-primary)] text-[var(--dg-text-primary)] shadow-sm'
+                : 'text-[var(--dg-text-muted)] hover:text-[var(--dg-text-secondary)]'
+            }`}
+          >
+            <span>{tab.icon}</span>
+            {tab.label}
+          </button>
+        ))}
+      </div>
+
+      {/* 内容区 */}
+      <div>
+        {activeTab === 'rules' && <AuditRulesPage />}
+        {activeTab === 'announcement' && <AnnouncementPage />}
+        {activeTab === 'notification' && <NotificationPage />}
+        {activeTab === 'ldap' && <LdapConfigPage />}
+      </div>
+    </div>
+  );
+}