Returns all active listings for the authenticated user. Each listing includes
property details, location information, current settings, and (when connected)
per-channel external IDs under channels (e.g. Airbnb listing id, Booking.com property id).
For direct booking, channels.direct lists only enabled sites with public URLs.

If both startDate and endDate query parameters are provided, the endpoint will
filter listings to only return those that are available for the specified date range.
This includes checking for blocked dates, minimum night requirements, and pricing availability.

Authentication: Pass either Authorization: Bearer <token> (OAuth 2.0) or the legacy authToken header.