first implementation - image/drawing integration

backend/src/main/java/com/aiteacher/document/SectionRepository.java

@@ -0,0 +1,11 @@
+package com.aiteacher.document;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface SectionRepository extends JpaRepository<SectionEntity, String> {
+    List<SectionEntity> findAllByBookId(UUID bookId);
+    void deleteAllByBookId(UUID bookId);
+}