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/lib/mock.ts

@@ -31,12 +31,10 @@ export const menuItems = [
   { id: 'roles', label: '角色权限', icon: 'UserCog', section: 'permission', roles: ['admin'] },
   { id: 'users', label: '用户管理', icon: 'Users', section: 'permission', roles: ['admin'] },
   { id: 'data-permission', label: '数据权限', icon: 'Lock', section: 'permission', roles: ['admin', 'dba'] },
-  { id: 'audit-rules', label: '审核规则', icon: 'Shield', section: 'system', roles: ['admin', 'dba'] },
   { id: 'audit-logs', label: '审计日志', icon: 'FileText', section: 'system', roles: ['admin', 'dba'] },
   { id: 'workflow', label: '审批流程', icon: 'GitBranch', section: 'system', roles: ['admin', 'dba'] },
   { id: 'auto-task', label: '自动任务', icon: 'Clock', section: 'system', roles: ['admin'] },
-  { id: 'announcement', label: '公告管理', icon: 'Megaphone', section: 'system', roles: ['admin'] },
-  { id: 'config-platform', label: '配置平台', icon: 'Settings', section: 'config', roles: ['admin'] },
+  { id: 'settings', label: '系统设置', icon: 'Settings', section: 'config', roles: ['admin'] },
 ];
 
 export const currentUser = {