fix(auth): update terminology to 'sign in' and 'sign out' (#20892)

Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/commands/authCommand.ts

@@ -14,8 +14,9 @@ import { clearCachedCredentialFile } from '@google/gemini-cli-core';
 import { SettingScope } from '../../config/settings.js';
 
 const authLoginCommand: SlashCommand = {
-  name: 'login',
-  description: 'Login or change the auth method',
+  name: 'signin',
+  altNames: ['login'],
+  description: 'Sign in or change the authentication method',
   kind: CommandKind.BUILT_IN,
   autoExecute: true,
   action: (_context, _args): OpenDialogActionReturn => ({
@@ -25,8 +26,9 @@ const authLoginCommand: SlashCommand = {
 };
 
 const authLogoutCommand: SlashCommand = {
-  name: 'logout',
-  description: 'Log out and clear all cached credentials',
+  name: 'signout',
+  altNames: ['logout'],
+  description: 'Sign out and clear all cached credentials',
   kind: CommandKind.BUILT_IN,
   action: async (context, _args): Promise<LogoutActionReturn> => {
     await clearCachedCredentialFile();