first implementation - image/drawing integration

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

@@ -0,0 +1,58 @@
+package com.aiteacher.document;
+
+import jakarta.persistence.*;
+import java.io.Serializable;
+import java.util.Objects;
+import java.util.UUID;
+
+@Entity
+@Table(name = "chunk_figure_ref")
+@IdClass(ChunkFigureRefEntity.PK.class)
+public class ChunkFigureRefEntity {
+
+    @Id
+    @Column(name = "chunk_id", nullable = false)
+    private UUID chunkId;
+
+    @Id
+    @Column(name = "figure_id", nullable = false, length = 200)
+    private String figureId;
+
+    @Column(name = "mention_page")
+    private Integer mentionPage;
+
+    public ChunkFigureRefEntity() {}
+
+    public ChunkFigureRefEntity(UUID chunkId, String figureId, Integer mentionPage) {
+        this.chunkId = chunkId;
+        this.figureId = figureId;
+        this.mentionPage = mentionPage;
+    }
+
+    public UUID getChunkId() { return chunkId; }
+    public String getFigureId() { return figureId; }
+    public Integer getMentionPage() { return mentionPage; }
+
+    public static class PK implements Serializable {
+        private UUID chunkId;
+        private String figureId;
+
+        public PK() {}
+        public PK(UUID chunkId, String figureId) {
+            this.chunkId = chunkId;
+            this.figureId = figureId;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (!(o instanceof PK pk)) return false;
+            return Objects.equals(chunkId, pk.chunkId) && Objects.equals(figureId, pk.figureId);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(chunkId, figureId);
+        }
+    }
+}