feat: unify moba workspace and persist session tree layout

backend/src/main/java/com/sshmanager/entity/SessionTreeLayout.java

@@ -0,0 +1,34 @@
+package com.sshmanager.entity;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+import javax.persistence.Column;
+import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
+import javax.persistence.Id;
+import javax.persistence.Table;
+import java.time.Instant;
+
+@Data
+@NoArgsConstructor
+@AllArgsConstructor
+@Entity
+@Table(name = "session_tree_layouts")
+public class SessionTreeLayout {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(nullable = false, unique = true)
+    private Long userId;
+
+    @Column(nullable = false, columnDefinition = "CLOB")
+    private String layoutJson;
+
+    @Column(nullable = false)
+    private Instant updatedAt = Instant.now();
+}