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/components/Layout.tsx

@@ -6,7 +6,6 @@ import {
 } from 'lucide-react';
 import { menuSections } from '@/lib/mock';
 import { useAuth } from '@/hooks/useAuth';
-import type { UserRole } from '@/hooks/useAuth';
 import { useTheme } from '@/hooks/useTheme';
 
 const iconMap: Record<string, React.ElementType> = {
@@ -15,15 +14,8 @@ const iconMap: Record<string, React.ElementType> = {
   Settings, Clock, Megaphone,
 };
 
-const roleBadgeStyle: Record<UserRole, string> = {
-  admin: 'bg-purple-500/15 text-purple-400',
-  dba: 'bg-blue-500/15 text-blue-400',
-  developer: 'bg-green-500/15 text-green-400',
-  guest: 'bg-gray-500/15 text-gray-400',
-};
-
 export default function Layout() {
-  const { user, logout, switchRole, visibleMenuItems } = useAuth();
+  const { user, logout, visibleMenuItems } = useAuth();
   const { theme, toggleTheme } = useTheme();
   const location = useLocation();
   const navigate = useNavigate();
@@ -34,18 +26,6 @@ export default function Layout() {
     return item?.label || '仪表盘';
   };
 
-  const toggleRole = () => {
-    const roles: UserRole[] = ['admin', 'dba', 'developer', 'guest'];
-    const idx = roles.indexOf(user.role);
-    const nextRole = roles[(idx + 1) % roles.length];
-    switchRole(nextRole);
-    // 切换角色后如果当前页面无权限，自动跳仪表盘
-    const allowed = visibleMenuItems.find(m => m.id === currentPath);
-    if (!allowed && currentPath !== 'dashboard') {
-      navigate('/dashboard', { replace: true });
-    }
-  };
-
   return (
     <div className="flex h-screen bg-[var(--dg-bg-primary)] text-[var(--dg-text-primary)] overflow-hidden">
       {/* 侧边栏 */}
@@ -102,21 +82,6 @@ export default function Layout() {
 
         {/* 底部 */}
         <div className="p-4 border-t border-[var(--dg-border)]">
-          {/* 角色切换演示 */}
-          <div className="mb-3 px-3 py-2 rounded-lg bg-[var(--dg-bg-tertiary)] border border-[var(--dg-border)]">
-            <div className="flex items-center justify-between">
-              <span className="text-xs text-[var(--dg-text-muted)]">当前角色</span>
-              <span className={`text-xs font-medium px-2 py-0.5 rounded ${roleBadgeStyle[user.role]}`}>
-                {user.roleName}
-              </span>
-            </div>
-            <button
-              onClick={toggleRole}
-              className="mt-2 w-full text-center text-[11px] text-[var(--dg-text-muted)] hover:text-blue-400 transition-colors py-1 rounded hover:bg-[var(--dg-bg-hover)]"
-            >
-              [演示] 切换角色
-            </button>
-          </div>
           <div className="flex items-center gap-3 p-2 rounded-lg hover:bg-[var(--dg-bg-hover)] cursor-pointer transition-colors">
             <div className="w-9 h-9 rounded-full dg-gradient-br flex items-center justify-center text-white font-semibold text-sm flex-shrink-0">
               {user.avatar}
@@ -145,8 +110,7 @@ export default function Layout() {
             <span className="text-[var(--dg-text-primary)] font-medium">{getPageTitle()}</span>
           </div>
           <div className="flex items-center gap-3">
-            {/* 角色标签 */}
-            <span className={`px-2.5 py-1 rounded-md text-xs font-medium ${roleBadgeStyle[user.role]}`}>
+            <span className="px-2.5 py-1 rounded-md text-xs font-medium bg-blue-500/15 text-blue-400">
               {user.roleName}
             </span>
             <button