Change the sender on the drafts waiting for approval

Point every not-yet-approved outgoing draft of a sequence at another connected Gmail (user_integration_id) so it sends from that mailbox. Approved drafts already queued to send are left alone and counted in skipped_approved. A follow-up that continues a Gmail thread stays on the mailbox that owns the thread (skipped_threaded), and a draft whose mailbox was disconnected stays put because nobody can vouch for the signature it carries (skipped_unknown_signer); regenerate either to move it. The mailbox must belong to a member of the active workspace, be able to send, and be owned by the same person whose name and signature the drafts carry.