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

frontend/vite.config.ts

@@ -1,5 +1,4 @@
-/// <reference types="vitest" />
-import { defineConfig } from 'vite'
+import { defineConfig } from 'vitest/config'
 import react, { reactCompilerPreset } from '@vitejs/plugin-react'
 import babel from '@rolldown/plugin-babel'