enhance rag retrieval + summary

backend/src/main/java/com/aiteacher/topic/TopicSummaryResponse.java

@@ -2,8 +2,11 @@ package com.aiteacher.topic;
 
 import java.time.Instant;
 import java.util.List;
+import java.util.UUID;
 
 public record TopicSummaryResponse(
+    UUID id,
+    int summaryNumber,
     String topicId,
     String topicName,
     String summary,
@@ -11,6 +14,7 @@ public record TopicSummaryResponse(
     Instant generatedAt
 ) {
     public record SourceReference(
+        String bookId,
         String bookTitle,
         Integer page
     ) {