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)

backend/app/api/v1/router.py

@@ -1,6 +1,9 @@
 from fastapi import APIRouter
 
-from app.api.v1.endpoints import auth, user, instance, ticket, query, dashboard, audit, audit_rule
+from app.api.v1.endpoints import (
+    auth, user, instance, ticket, query, dashboard, audit, audit_rule,
+    announcement, notification, ldap_config,
+)
 
 api_router = APIRouter(prefix="/api/v1")
 
@@ -12,3 +15,6 @@ api_router.include_router(query.router)
 api_router.include_router(dashboard.router)
 api_router.include_router(audit.router)
 api_router.include_router(audit_rule.router)
+api_router.include_router(announcement.router)
+api_router.include_router(notification.router)
+api_router.include_router(ldap_config.router)