feat(auth): add user invitation flow with account setup

- add `createAccountSetup`, `verifyAccountSetupToken`, `deleteAccountSetupToken` to verifications core
- add `completeAccountSetup` function to auth core for password creation on invite
- add `InvitationEmail` template for sending invite links
- add `SetupAccountPage` client page for invited users to set their password
- add `UserCreateModal` admin component to invite new users
- wire invitation action and API endpoint in auth feature
- update admin `UsersPage` to include user creation modal
- update auth and admin README docs

src/features/auth/AuthPage.server.js

@@ -6,6 +6,7 @@ import {
   forgotPasswordAction,
   resetPasswordAction,
   verifyEmailAction,
+  setupAccountAction,
   setSessionCookie,
   getSession,
 } from './actions.js';
@@ -25,6 +26,7 @@ export default async function AuthPage({ params, searchParams }) {
           forgotPasswordAction={forgotPasswordAction}
           resetPasswordAction={resetPasswordAction}
           verifyEmailAction={verifyEmailAction}
+          setupAccountAction={setupAccountAction}
           setSessionCookieAction={setSessionCookie}
           redirectAfterLogin={process.env.ZEN_AUTH_REDIRECT_AFTER_LOGIN || '/'}
           currentUser={session?.user || null}