feat: harden the myep OAuth2 login

tests/Controller/DashboardControllerTest.php

@@ -70,7 +70,8 @@ class DashboardControllerTest extends WebTestCase
         $crawler = $this->client->request('GET', '/');
 
         self::assertCount(0, $crawler->filter('#mobilenav'));
-        self::assertCount(1, $crawler->filter('a[href="/logout"]'));
+        // The way out is a form, not a link: the firewall's logout is CSRF-protected.
+        self::assertCount(1, $crawler->filter('form[action="/logout"]'));
     }
 
     public function testATileCountsWhatIsStillFreeToday(): void