gateway: create aggregated product + order dto

[pooranjoyb]

[Saranyadharani]

Hi @pooranjoyb,

I can create the aggregated product + order DTO for the gateway!

My approach:

1. Create OrderWithProduct DTO combining order and product data
2. Add proper validation and serialization
3. Ensure efficient data aggregation (avoid N+1 queries)
4. Add TypeScript interfaces for type safety

Please assign this to me. Thanks!