test: expand coverage, dedupe data-driven tests, extract shared WebTestCase base

- Add #[CoversClass] to Base64Test and FilenameSanitizerTest
- Merge near-duplicate test methods into #[DataProvider] cases across
  ResetPasswordControllerTest, SettingsControllerTest, ClaimSeasonCommandTest,
  FilenameSanitizerTest, Base64Test, and SeasonRepositoryTest
- Add integration tests for previously untested controllers: public
  QuizController (quiz-taking flow), LoginController, RegistrationController,
  EliminationController, and PrepareEliminationController
- Add unit tests for Elimination and BankQuestion entity logic
- Extract shared WebTestCase setup/helpers (client, entityManager, login,
  entity lookups, CSRF token scraping) into AbstractControllerWebTestCase,
  removing duplicated boilerplate from all 14 WebTestCase files

tests/Controller/WellKnownControllerTest.php

@@ -6,21 +6,12 @@ namespace Tvdt\Tests\Controller;
 
 use PHPUnit\Framework\Attributes\CoversClass;
 use Safe\DateTimeImmutable;
-use Symfony\Bundle\FrameworkBundle\KernelBrowser;
-use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
 use Symfony\Component\HttpFoundation\Request;
 use Tvdt\Controller\WellKnownController;
 
 #[CoversClass(WellKnownController::class)]
-final class WellKnownControllerTest extends WebTestCase
+final class WellKnownControllerTest extends AbstractControllerWebTestCase
 {
-    private KernelBrowser $client;
-
-    protected function setUp(): void
-    {
-        $this->client = self::createClient();
-    }
-
     public function testChangePasswordRedirectsToSettings(): void
     {
         $this->client->request(Request::METHOD_GET, '/.well-known/change-password');