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/App.tsx

@@ -13,8 +13,7 @@ import DataPermissionPage from '@/pages/DataPermissionPage';
 import AuditRulesPage from '@/pages/AuditRulesPage';
 import WorkflowPage from '@/pages/WorkflowPage';
 import AutoTaskPage from '@/pages/AutoTaskPage';
-import AnnouncementPage from '@/pages/AnnouncementPage';
-import ConfigPlatformPage from '@/pages/ConfigPlatformPage';
+import SettingsPage from '@/pages/SettingsPage';
 import AuditLogsPage from '@/pages/AuditLogsPage';
 
 // 路由守卫：未登录跳转登录页，无权限跳转仪表盘
@@ -64,8 +63,7 @@ function AppRoutes() {
           <Route path="audit-logs" element={<AuditLogsPage />} />
           <Route path="workflow" element={<WorkflowPage />} />
           <Route path="auto-task" element={<AutoTaskPage />} />
-          <Route path="announcement" element={<AnnouncementPage />} />
-          <Route path="config-platform" element={<ConfigPlatformPage />} />
+          <Route path="settings" element={<SettingsPage />} />
           <Route path="*" element={<Navigate to="/dashboard" replace />} />
         </Route>
       </Route>