Backend Feature: GetCart

User story

As a visitor, I want to see the contents of my cart so that I can review my items before checking out.

Dependencies

• Entities: Cart, CartItem, Product
• API specs: GET /cart/:sessionId

Acceptance criteria

• [ ] Returns the open cart for the given sessionId; returns 404 if none exists.
• [ ] Each item includes id, quantity, and product details (id, name, price, photoUrl).
• [ ] photoUrl is the full public URL of the first non-deleted product photo, or null if none.

Edge cases

• No open cart for sessionId: returns 404.
• Product in cart has no photos: photoUrl is null.

Notes

• Only the open cart is returned — closed carts are not exposed by this endpoint.