docs: translate partial comments to Chinese

src/model/LeaveRequest.java

@@ -21,13 +21,13 @@ public class LeaveRequest {
     private Date requestTime;        // 申请时间
     private Date approvalTime;       // 审批时间
 
-    // Constructors
+    // 构造方法
     public LeaveRequest() {
         this.status = ApprovalStatus.PENDING;
         this.requestTime = new Date();
     }
 
-    // Getters and Setters
+    // Getters 和 Setters 方法
     public int getId() {
         return id;
     }

src/model/Student.java

@@ -13,7 +13,7 @@ public class Student {
     private String major;        // 专业
     private String password;      // 登录密码
 
-    // Constructors
+    // 构造方法
     public Student() {}
 
     public Student(String studentId, String name, String className, String contact, String college, String major) {
@@ -35,7 +35,7 @@ public class Student {
         this.password = password;
     }
 
-    // Getters and Setters
+    // Getters 和 Setters 方法
     public int getId() {
         return id;
     }

src/model/Teacher.java

@@ -11,7 +11,7 @@ public class Teacher {
     private String contact;      // 联系方式
     private String password;     // 登录密码
 
-    // Constructors
+    // 构造方法
     public Teacher() {}
 
     public Teacher(String teacherId, String name, String department, String contact) {
@@ -29,7 +29,7 @@ public class Teacher {
         this.password = password;
     }
 
-    // Getters and Setters
+    // Getters 和 Setters 方法
     public int getId() {
         return id;
     }