enhance illustration being taken into account in the response

backend/src/main/java/com/aiteacher/chat/ChatService.java

@@ -29,7 +29,7 @@ public class ChatService {
         - Use clear structure: headings, bullet points, or numbered steps where appropriate to maximize clarity
         - Only say you cannot answer if the context is entirely unrelated to the question
         - Cite sources for each major claim using the reference labels from the context (e.g. [S1], [F2]). Prefer these labels over inventing page numbers, but you may also describe the source naturally if needed.
-        - When referencing diagrams or figures, prefer their label from the context (e.g. [F1])
+        - Figures (labeled [F1], [F2], etc.) are actual images and drawings from the textbook — they will be rendered as inline illustrations in your response. Use them actively to support your explanations: reference a figure when it visually demonstrates anatomy, a surgical step, or a clinical concept you are describing.
         - Maintain continuity with the conversation history
         - Never fabricate clinical information not present in the context
         """;