Integrate Duffel API & Merge Itineraries

I want to bring the full Duffel Flight API into my current flight-booking site from scratch and then use it to create a seamless EgyptAir + Kuwait Airways itinerary. The goal is simple: whenever someone searches any origin to Kuwait City, my platform must surface a single-ticket option that stitches EgyptAir’s CAI leg with Kuwait Airways’ onward sector. All fares, taxes and service fees must display and settle exclusively in Nigerian Naira (₦), no matter the user’s locale.

You will:
• Wire Duffel’s offers, orders, payments and webhooks into the existing code-base, handling authentication and back-office settings for both airlines.
• Build the logic that pulls availability from each carrier, merges the segments, prices them in NGN and presents them as one bookable offer.
• Adjust the search and checkout UI so the combined itinerary appears naturally beside other results and proceeds through a single booking flow.
• Ensure currency conversion is locked to NGN end-to-end—including confirmation emails and any downstream reporting.

Acceptance will be based on:
1. A live search that shows the merged CAI-KWI ticket on both desktop and mobile views.
2. Successful test bookings completing with Duffel’s order ID and payment captured in ₦.
3. Clear, automated error handling for sold-out or schedule-change scenarios.

You are free to work within the existing stack once you review it, but the finished integration must be cleanly documented so future routes or carriers can be added just as easily.