feat: 查询页增强 + 权限体系优化

- Redis DB0~DB15 下拉选择，默认DB0
- 查询历史粘贴按钮（一键填入SQL编辑器）
- 去掉导出历史按钮
- SchemaSidebar 按目标数据库筛选
- SQL自动补全 schema 双层注册（db→tables, table→columns）
- 后端 db-schema 接口（INFORMATION_SCHEMA.COLUMNS 一次加载）
- autocompletion 扩展激活
- Redis key 树形结构（冒号分隔层级）
- Redis 查询模板 GET/HGETALL/HGET
- guest 角色彻底移除，改为 auditor
- 登录页优化：去掉演示账号、placeholder 中文提示

frontend/src/hooks/useAuth.tsx

@@ -3,15 +3,15 @@ import { menuItems } from '@/constants/menu';
 
 const defaultUser = {
   id: 0,
-  username: 'guest',
+  username: '',
   email: '',
-  role: 'guest' as const,
-  roleName: '访客',
-  avatar: 'G',
+  role: 'developer' as const,
+  roleName: '',
+  avatar: '',
 };
 import { authApi } from '@/api/auth';
 
-export type UserRole = 'admin' | 'dba' | 'developer' | 'guest';
+export type UserRole = 'admin' | 'dba' | 'developer' | 'auditor';
 
 /** 细粒度权限类型 */
 export type PermissionAction =
@@ -98,7 +98,7 @@ const roleNameMap: Record<UserRole, string> = {
   admin: '超级管理员',
   dba: '数据库管理员',
   developer: '开发人员',
-  guest: '访客',
+  auditor: '审计员',
 };
 
 /** 角色权重映射，用于权限级别比较 */
@@ -106,16 +106,16 @@ const roleWeightMap: Record<UserRole, number> = {
   admin: 100,
   dba: 80,
   developer: 60,
-  guest: 20,
+  auditor: 40,
 };
 
 const routePermissionMap: Record<string, UserRole[]> = {
-  dashboard: ['admin', 'dba', 'developer', 'guest'],
+  dashboard: ['admin', 'dba', 'developer', 'auditor'],
   instances: ['admin', 'dba'],
   'instance-groups': ['admin'],
   'data-dictionary': ['admin', 'dba', 'developer'],
-  tickets: ['admin', 'dba', 'developer'],
-  queries: ['admin', 'dba', 'developer', 'guest'],
+  tickets: ['admin', 'dba', 'developer', 'auditor'],
+  queries: ['admin', 'dba', 'developer'],
   roles: ['admin'],
   users: ['admin'],
   'audit-logs': ['admin', 'dba'],
@@ -130,7 +130,7 @@ export const actionPermissionMap: Record<string, UserRole[]> = {
   'ticket.execute': ['admin', 'dba'],
   'ticket.rollback': ['admin', 'dba'],
   'ticket.delete': ['admin'],
-  'query.create': ['admin', 'dba', 'developer', 'guest'],
+  'query.create': ['admin', 'dba', 'developer'],
   'query.export': ['admin', 'dba', 'developer'],
   'instance.add': ['admin', 'dba'],
   'instance.edit': ['admin', 'dba'],
@@ -451,7 +451,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
     isAdmin: user.role === 'admin',
     isDBA: user.role === 'dba',
     isDeveloper: user.role === 'developer',
-    isGuest: user.role === 'guest',
+    isGuest: user.role === 'auditor',
     hasRoleLevel,
   }), [user, isLoggedIn, login, logout, switchRole, hasPermission, hasActionPermission,
        hasDataSourcePermission, checkDataSourcePermissions, refreshPermissions,