List Hubspot Email Inboxes

The portal's inboxes, plus whether there is a portal at all.

A workspace with no HubSpot connection is an ordinary state, not an error — returning 4xx for it makes the generated client throw and pops a red toast at someone who has simply not connected HubSpot. The flag lets the UI say "connect it under Integrations" instead of an empty list, which would read as "you have no inboxes".