fix: natural follow-up conversation flow

- Grader: separate followup hint from scoring feedback
- Interviewer: use followup hint directly without prefix/suffix
- Restored standard and choice question presentation paths

server/src/assessment/graph/nodes/grader.node.ts

@@ -252,10 +252,15 @@ Format your response as JSON:
       shouldFollowUp = false;
     }
 
+    let followupHintMsg: AIMessage | null = null;
     if (shouldFollowUp && followupHints.length > 0) {
       const hint = followupHints[Math.min(currentFollowUpCount, followupHints.length - 1)];
-      const hintLabel = isZh ? '追问方向' : isJa ? '追加の方向性' : 'Follow-up hint';
-      enhancedFeedback = `${result.feedback}\n\n${hintLabel}: ${hint}`;
+      const hintLabel = isZh
+        ? `让我帮你完善一下：${hint}`
+        : isJa
+          ? `もう少し詳しく伺います：${hint}`
+          : `Let me help you elaborate: ${hint}`;
+      followupHintMsg = new AIMessage(hintLabel);
     }
 
     const feedbackMessage = new AIMessage(
@@ -271,8 +276,12 @@ Format your response as JSON:
       saysIDontKnow,
     });
 
+    const feedbackHistoryMessages = followupHintMsg
+      ? [feedbackMessage, followupHintMsg]
+      : [feedbackMessage];
+
     return {
-      feedbackHistory: [feedbackMessage],
+      feedbackHistory: feedbackHistoryMessages,
       scores: newScores,
       shouldFollowUp: shouldFollowUp,
       followUpCount: shouldFollowUp ? currentFollowUpCount + 1 : 0,