API access to public guest review summaries

Right now the guest review summary that shows in the Hospitable UI isn't available through the API. For operators running fraud and trust-and-safety checks at volume, this is the missing piece.

The use case: when a new booking comes in, we want to automatically cross-reference the guest against their review history, both reviews they've left and reviews hosts have left about them, to flag repeat problem guests before check-in. We can build the whole workflow except this step, because the review summary data the UI already displays isn't exposed to the API. That forces a manual check on every high-volume booking, which doesn't scale past a handful of properties.

Impact: any multi-property operator doing automated guest screening hits this wall. Exposing the review summary through the API (or a webhook on new bookings that includes it) would let us run real-time, automated trust checks instead of manual spot-checks.