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/deposits/dto/deposit.dto.ts

@@ -1,4 +1,5 @@
-import { IsInt, IsNumber, IsString, IsOptional } from 'class-validator';
+import { IsInt, IsNumber, IsString, IsOptional, ValidateNested } from 'class-validator';
+import { Type } from 'class-transformer';
 
 export class CreateDepositDto {
   @IsInt()
@@ -15,6 +16,25 @@ export class CreateDepositDto {
   notes?: string;
 }
 
+export class CreateInstallmentDto {
+  @IsNumber()
+  amount: number;
+
+  @IsString()
+  dueDate: string;
+}
+
+export class UpdateInstallmentDto {
+  @IsOptional()
+  @IsString()
+  paidDate?: string;
+
+  @IsOptional()
+  @IsString()
+  status?: string;
+}
+
+
 export class RefundDepositDto {
   @IsString()
   refundDate: string;
@@ -31,3 +51,15 @@ export class RefundDepositDto {
   @IsString()
   notes?: string;
 }
+export class CreateDepositWithInstallmentsDto extends CreateDepositDto {
+  @IsOptional()
+  @ValidateNested({ each: true })
+  @Type(() => CreateInstallmentDto)
+  installments?: CreateInstallmentDto[];
+}
+
+export class ApproveRefundDto {
+  @IsOptional()
+  @IsString()
+  notes?: string;
+}