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/constants/menu.ts

@@ -8,11 +8,11 @@ export const menuSections = [
 ];
 
 export const menuItems = [
-  { id: 'dashboard', label: '仪表盘', icon: 'LayoutDashboard', section: 'overview', roles: ['admin', 'dba', 'developer', 'guest'] },
+  { id: 'dashboard', label: '仪表盘', icon: 'LayoutDashboard', section: 'overview', roles: ['admin', 'dba', 'developer', 'auditor'] },
   { id: 'instances', label: '数据源', icon: 'Database', section: 'datasource', roles: ['admin', 'dba'] },
   { id: 'instance-groups', label: '权限管理', icon: 'Lock', section: 'permission', roles: ['admin'] },
-  { id: 'tickets', label: '数据变更', icon: 'ClipboardList', section: 'ticket', roles: ['admin', 'dba', 'developer'] },
-  { id: 'queries', label: '查询数据', icon: 'Search', section: 'ticket', roles: ['admin', 'dba', 'developer', 'guest'] },
+  { id: 'tickets', label: '数据变更', icon: 'ClipboardList', section: 'ticket', roles: ['admin', 'dba', 'developer', 'auditor'] },
+  { id: 'queries', label: '查询数据', icon: 'Search', section: 'ticket', roles: ['admin', 'dba', 'developer'] },
   { id: 'roles', label: '角色权限', icon: 'UserCog', section: 'permission', roles: ['admin'] },
   { id: 'users', label: '用户管理', icon: 'Users', section: 'permission', roles: ['admin'] },
   { id: 'audit-logs', label: '审计日志', icon: 'FileText', section: 'system', roles: ['admin', 'dba'] },