fix: the exam's top bar stays put while the question scrolls

Only the question scrolls in the middle column now. The bar carrying the item
counter and the tools was inside the scrolling area, so it went up with a long
stem — exactly when you wanted it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TqXevQJhxFrM7jJg82cgZN

frontend/src/pages/QuizPage.jsx

@@ -1705,7 +1705,7 @@ const timerStarted = timeLeft !== null
             onClick={() => setRailOpen(true)}>›</button>
         )}
         {/* Main content */}
-        <div style={{ flex: 1, minWidth: 0 }}>
+        <div className="quiz-main">
           <div className="quiz-topbar">
             {examChrome ? (
               <>

frontend/src/pages/QuizPlayer.css

@@ -343,6 +343,19 @@ body:has(.quiz-player.is-boxed) .navbar { margin-bottom: 0; }
 /* Each column scrolls on its own. `min-height: 0` is what lets a grid child
    shrink below its content and become scrollable at all. */
 .quiz-player.is-boxed .quiz-layout > * { min-height: 0; overflow-y: auto; }
+
+/* The middle column is itself two parts: the bar that says where you are, and
+   the question under it. Only the question scrolls — the bar used to go up
+   with it, so the item counter and the tools left the screen exactly when a
+   long stem made you want them. */
+.quiz-main { flex: 1; min-width: 0; }
+.quiz-player.is-boxed .quiz-main {
+  display: flex; flex-direction: column; overflow: hidden;
+}
+.quiz-player.is-boxed .quiz-main > .quiz-topbar { flex: none; }
+.quiz-player.is-boxed .quiz-main > *:not(.quiz-topbar) {
+  flex: 1; min-height: 0; overflow-y: auto;
+}
 .quiz-player.is-boxed .quiz-sidebar { position: static; max-height: none; }
 
 .quiz-footbar {

frontend/src/pages/ResultsPage.jsx

@@ -155,7 +155,7 @@ export default function ResultsPage() {
             onClick={() => setRailOpen(true)}>›</button>
         )}
 
-        <div style={{ flex: 1, minWidth: 0 }}>
+        <div className="quiz-main">
           <div className="quiz-topbar">
             <p className="quiz-question-select is-static">
               <small>Question</small><strong>{current + 1}</strong> of {answers.length}