P2-14: Deposit installment tracking + refund approval flow

- Add DepositInstallment entity (id, depositId, amount, dueDate, paidDate, status, createdAt)
- Add installments OneToMany relation to Deposit entity with cascade+eager
- Add refund approval fields: refundStatus, refundRequestedAt, refundApprovedBy, refundApprovedAt
- Add installment DTOs (CreateInstallmentDto, UpdateInstallmentDto)
- Add refund approval DTOs (ApproveRefundDto, CreateDepositWithInstallmentsDto)
- Service: add/create/update/delete installments, requestRefund, approveRefund, findPendingRefunds
- Controller: GET deposits/:id, GET pending-refunds, POST :id/installments, PUT installments/:id, DELETE installments/:id, POST :id/request-refund, PUT :id/approve-refund
- Frontend: detail modal with installment list, refund request button, pending refunds tab with approve actions

apps/server/src/entities/deposit-installment.entity.ts

@@ -0,0 +1,37 @@
+import {
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  ManyToOne,
+  JoinColumn,
+} from 'typeorm';
+import { Deposit } from './deposit.entity';
+
+@Entity('deposit_installments')
+export class DepositInstallment {
+  @PrimaryGeneratedColumn()
+  id: number;
+
+  @Column({ name: 'deposit_id' })
+  depositId: number;
+
+  @Column({ type: 'decimal', precision: 10, scale: 2 })
+  amount: number;
+
+  @Column({ name: 'due_date', type: 'date' })
+  dueDate: string;
+
+  @Column({ name: 'paid_date', type: 'date', nullable: true })
+  paidDate: string;
+
+  @Column({ type: 'varchar', length: 20, default: 'pending' })
+  status: string; // pending | paid
+
+  @CreateDateColumn({ name: 'created_at' })
+  createdAt: Date;
+
+  @ManyToOne(() => Deposit, (d) => d.installments, { onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'deposit_id' })
+  deposit: Deposit;
+}

apps/server/src/entities/deposit.entity.ts

@@ -4,9 +4,11 @@ import {
   Column,
   CreateDateColumn,
   ManyToOne,
+  OneToMany,
   JoinColumn,
 } from 'typeorm';
 import { Student } from './student.entity';
+import { DepositInstallment } from './deposit-installment.entity';
 
 @Entity('deposits')
 export class Deposit {
@@ -44,10 +46,26 @@ export class Deposit {
   @Column({ name: 'recorded_by', nullable: true })
   recordedBy: number;
 
+  @Column({ name: 'refund_status', length: 30, nullable: true })
+  refundStatus: string | null; // pending | head_teacher_approved | finance_approved | refunded
+
+  @Column({ name: 'refund_requested_at', nullable: true })
+  refundRequestedAt: Date | null;
+
+  @Column({ name: 'refund_approved_by', type: 'integer', nullable: true })
+  refundApprovedBy: number | null;
+
+  @Column({ name: 'refund_approved_at', nullable: true })
+  refundApprovedAt: Date | null;
+
+  @OneToMany(() => DepositInstallment, (i) => i.deposit, { cascade: true, eager: true })
+  installments: DepositInstallment[];
+
   @CreateDateColumn({ name: 'created_at' })
   createdAt: Date;
 
   @ManyToOne(() => Student, { eager: true })
   @JoinColumn({ name: 'student_id' })
   student: Student;
+
 }

apps/server/src/entities/index.ts

@@ -8,6 +8,7 @@ export { BillItem } from './bill-item.entity';
 export { User } from './user.entity';
 export { OperationLog } from './operation-log.entity';
 export { Deposit } from './deposit.entity';
+export { DepositInstallment } from './deposit-installment.entity';
 export { Classroom } from './classroom.entity';
 export { Tenant } from './tenant.entity';
 export { ClassroomRental } from './classroom-rental.entity';