Get Chat Share State

Surfaces the chat's current share state so the modal can open in the right mode (share-vs-revoke) without an extra round-trip.

The three counts power the consent-disclosure block above the toggle so the owner sees exactly what they're about to expose. They reflect live state — sharing is live (not snapshot-at-enable), so these numbers are also a lower bound for what subsequent viewers will see if more messages / runs / files land before revocation.