[MR Train 1/6] Refactor: Add foundation interfaces and DTOs

MR Train Overview

This is MR 1 of 6 in a stacked MR train to refactor orders-service.

Train Structure

1. [MR 1/6] Foundation ← YOU ARE HERE
2. [MR 2/6] Database layer (depends on MR 1)
3. [MR 3/6] Service layer (depends on MR 2)
4. [MR 4/6] API endpoints (depends on MR 3)
5. [MR 5/6] Integration tests (depends on MR 4)
6. [MR 6/6] Performance optimizations (depends on MR 5)

This MR: Foundation

Adds the foundational interfaces and domain models for the refactored orders-service.

Changes

• Created Order domain model with Lombok
• Added OrderStatus enum
• Defined OrderRepository interface
• Created standardized DTOs for API requests

Why This Approach?

Breaking the refactoring into small, reviewable chunks makes it easier to:

• Review incrementally
• Catch issues early
• Roll back specific changes if needed
• Allow parallel work on dependent features

Next Steps

Once this merges, MR 2 will implement the database layer using these interfaces.

@sabrina_farmer @bill_staples Please review when you have a chance!