feat(session): preserve intended URL across session timeout and add expiry warning dialog

When a session expires, the user's current URL is now captured and restored
after re-authentication (via remember-me cookie or manual login), instead of
always redirecting to the dashboard. A JavaScript session warning dialog
appears ~2 minutes before idle timeout, allowing users to extend their session
with a single click. Includes open-redirect prevention via URL validation,
Microsoft SSO callback support, and 33 unit tests.

Refs: SESSION-REDIRECT-PRESERVE-001

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

pages/auth/microsoft/callback().php

@@ -1,5 +1,6 @@
 <?php
 
+use MintyPHP\Http\IntendedUrlService;
 use MintyPHP\Http\SessionStoreInterface;
 use MintyPHP\Router;
 use MintyPHP\Service\Auth\AuthServicesFactory;
@@ -66,4 +67,5 @@ if ($tenantSsoService->shouldAutoRememberOnMicrosoftLogin($tenantId)) {
     $authServicesFactory->createRememberMeService()->rememberUser($userId);
 }
 
-Router::redirect('admin');
+$intendedUrlService = app(IntendedUrlService::class);
+Router::redirect($intendedUrlService->retrieveAndForget($sessionStore));