first implementation

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

@@ -0,0 +1,18 @@
+package com.aiteacher.topic;
+
+import java.time.Instant;
+import java.util.List;
+
+public record TopicSummaryResponse(
+    String topicId,
+    String topicName,
+    String summary,
+    List<SourceReference> sources,
+    Instant generatedAt
+) {
+    public record SourceReference(
+        String bookTitle,
+        Integer page
+    ) {
+    }
+}