增强 SSH/SFTP 稳定性并完善安全校验与前端交互

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

@@ -6,6 +6,7 @@ import lombok.AllArgsConstructor;
 
 import javax.persistence.*;
 import java.time.Instant;
+import java.time.temporal.ChronoUnit;
 
 @Data
 @NoArgsConstructor
@@ -32,4 +33,7 @@ public class User {
 
     @Column(nullable = false)
     private Instant updatedAt = Instant.now();
+
+    @Column(nullable = false)
+    private Instant passwordChangedAt;
 }