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;
+}