Add round-trip date validation and 12-month booking window

Fix auth cookie not sent in HF Spaces iframe context

Fix auth token invalidated on server restart

Add flight booking flow with payment validation

Add HF Spaces deployment config and passkey auth

Add Google Flights-style step-based round-trip booking flow

Add Google Flights-style "Best/Other" sections, emissions, rich detail view

Fix time+1 wrapping, add airline discount pricing, document fare engine

Add flight booking website (Google Flights clone)