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/hooks/useAuth.tsx

@@ -45,13 +45,10 @@ const routePermissionMap: Record<string, UserRole[]> = {
   roles: ['admin'],
   users: ['admin'],
   'data-permission': ['admin', 'dba'],
-  'audit-rules': ['admin', 'dba'],
   'audit-logs': ['admin', 'dba'],
   workflow: ['admin', 'dba'],
   'auto-task': ['admin'],
-  announcement: ['admin'],
-  'config-platform': ['admin'],
-  notifications: ['admin'],
+  settings: ['admin'],
 };
 
 export const actionPermissionMap: Record<string, UserRole[]> = {