feat: add ShortAnswer and MathInput renderers

frontend/src/components/questions/MathInput.tsx

@@ -0,0 +1,45 @@
+import { useState, useEffect } from 'react'
+import katex from 'katex'
+import type { Question } from '../../types'
+
+interface Props {
+  q: Question
+  value: string | null | undefined
+  onChange: (val: string) => void
+  locked?: boolean
+}
+
+// The KaTeX preview uses innerHTML: KaTeX controls all output, making this safe.
+export default function MathInput({ value = '', onChange, locked }: Props) {
+  const [preview, setPreview] = useState('')
+
+  useEffect(() => {
+    if (!value) { setPreview(''); return }
+    try {
+      setPreview(katex.renderToString(value, { throwOnError: false, displayMode: false }))
+    } catch {
+      setPreview('')
+    }
+  }, [value])
+
+  return (
+    <div className="answer-input-wrap">
+      <input
+        className="input mono"
+        type="text"
+        value={value ?? ''}
+        onChange={(e) => onChange(e.target.value)}
+        placeholder="LaTeX, e.g.  2x\ln x + x"
+        disabled={locked}
+        autoComplete="off"
+        spellCheck={false}
+      />
+      <div className="math-preview">
+        <span className="math-preview-label">Preview</span>
+        {preview
+          ? <span dangerouslySetInnerHTML={{ __html: preview }} />
+          : <span className="faint" style={{ fontSize: 13 }}>Live LaTeX preview appears here</span>}
+      </div>
+    </div>
+  )
+}

frontend/src/components/questions/ShortAnswer.tsx

@@ -0,0 +1,30 @@
+import type { Question } from '../../types'
+
+interface Props {
+  q: Question
+  value: string | null | undefined
+  onChange: (val: string) => void
+  locked?: boolean
+}
+
+export default function ShortAnswer({ q, value = '', onChange, locked }: Props) {
+  return (
+    <div className="answer-input-wrap">
+      <input
+        className="input"
+        type="text"
+        value={value ?? ''}
+        onChange={(e) => onChange(e.target.value)}
+        placeholder="Type your answer…"
+        disabled={locked}
+        autoComplete="off"
+        spellCheck={q.type === 'translation'}
+      />
+      {q.type === 'translation' && q.targetLanguage && (
+        <div className="faint mono" style={{ fontSize: 11 }}>
+          Answer in {q.targetLanguage}
+        </div>
+      )}
+    </div>
+  )
+}