Refactor Cart Types

[rohan24may]

I accidentally created a separate CartItem interface inside cartStore.ts instead of using the existing cart types architecture.

Currently:

• types/order.ts contains a CartItem interface.
• cartStore.ts contains another local CartItem interface:

interface CartItem {
item: MenuItem;
quantity: number;
}

This creates duplicate sources of truth.

Task 🔢 :

• Review both CartItem definitions.
• Decide whether the existing types/order.ts CartItem should be extended or the store structure should be updated.
• Refactor cartStore.ts to use shared types from types/order.ts.
• Remove the duplicate local CartItem interface.

Note : Current cart, checkout, and payment flows depend on the existing store structure, so this should be done carefully to avoid breaking those pages.