fix: resolve tsc-b build errors (Tex JSX type, Essay index sig, ExamRunner closure, vitest config)

frontend/src/App.tsx

@@ -95,7 +95,7 @@ export default function App() {
         <Landing onLoadExam={loadExam} history={history} onResume={resume} onClearHistory={clearAllHistory} onReviewAttempt={reviewAttempt} />
       )}
       {screen === 'exam' && exam && examState && (
-        <ExamRunner exam={exam} state={examState} setState={setExamState} onSubmit={submit} onExit={exit} />
+        <ExamRunner exam={exam} state={examState} setState={setExamState as React.Dispatch<React.SetStateAction<ExamState>>} onSubmit={submit} onExit={exit} />
       )}
       {(screen === 'results' || screen === 'review') && exam && examState && (
         <Results exam={exam} state={examState} onRestart={restart} onExit={exit} reviewOnly={screen === 'review'} />