refactor(auth): remove Guest role from user type system

Remove all references to 'Guest' user type from the codebase, simplifying the role system to only support 'Admin' and 'User' roles.

Changes:
- Update type definitions to exclude 'Guest' from UserType
- Remove isGuest() method from SessionManager
- Remove Guest-specific logic from update services
- Update all type assertions from 'Admin | User | Guest' to 'Admin | User'
- Remove Guest UI styling from UserSelectionDialog
- Replace Guest fallback with ValidationError in settings handler

Error handling:
- Zod schema now rejects 'Guest' as invalid user type
- TypeScript will fail compilation if 'Guest' is referenced
- Runtime errors occur if database contains Guest users

No database migration needed (confirmed: no Guest users exist)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/renderer/src/components/UserSelectionDialog.tsx

@@ -13,7 +13,7 @@ import { Modal } from './ui/Modal'
 export interface UserInfo {
   id: number
   username: string
-  userType: 'Admin' | 'User' | 'Guest'
+  userType: 'Admin' | 'User'
   createTime?: Date
 }
 
@@ -61,8 +61,7 @@ export const UserSelectionDialog: React.FC<UserSelectionDialogProps> = ({
 
   const userTypeStyles: Record<string, string> = {
     Admin: 'bg-amber-50 text-amber-600',
-    User: 'bg-blue-50 text-blue-600',
-    Guest: 'bg-gray-100 text-gray-600'
+    User: 'bg-blue-50 text-blue-600'
   }
 
   if (!isOpen) return null

src/renderer/src/components/app/UnauthenticatedApp.tsx

@@ -4,7 +4,7 @@ import UserSelectionDialog, { type UserInfo as SelectedUserInfo } from '../UserS
 
 interface CurrentUser {
   username: string
-  userType: 'Admin' | 'User' | 'Guest'
+  userType: 'Admin' | 'User'
 }
 
 interface UnauthenticatedAppProps {

src/renderer/src/hooks/useAppBootstrap.ts

@@ -17,7 +17,7 @@ export interface CurrentUser {
 export interface SelectedUserInfo {
   id: number
   username: string
-  userType: 'Admin' | 'User' | 'Guest'
+  userType: 'Admin' | 'User'
   computerName?: string
 }
 

src/renderer/src/hooks/useAuth.ts

@@ -3,7 +3,7 @@ import { useState, useCallback } from 'react'
 interface UserInfo {
   id: number
   username: string
-  userType: 'Admin' | 'User' | 'Guest'
+  userType: 'Admin' | 'User'
   computerName?: string
 }
 

src/renderer/src/stores/useUserStore.ts

@@ -10,7 +10,7 @@ import { create } from 'zustand'
 interface UserInfo {
   id: number
   username: string
-  userType: 'Admin' | 'User' | 'Guest'
+  userType: 'Admin' | 'User'
   computerName?: string
 }