Per-guest redemption limit for Direct booking promo codes

Problem: Promo code "Number of uses" limits apply to the whole code, not per guest. Hosts can't create one code that multiple guests can use, while still restricting each guest to a single redemption.

Current workaround: Hosts create a separate single-use code for each guest and share it individually.

Impact:

• Time-consuming to manage at scale
• Doesn't allow a single shareable code (e.g. a general "first Direct booking" promo) to be distributed broadly while still preventing repeat use by the same guest

Proposed solution: Add an option when creating a promo code to set a "per guest" or "per user" redemption limit (e.g. 1 use per guest), in addition to the existing total "Number of uses" setting.

Unlock: Hosts could run broad promotions (like first-time Direct booking discounts) using a single shareable code, without manually generating and tracking individual codes per guest.