Last-member protection on workspace and organization deletion

A few support tickets traced back to admins accidentally deleting their own seat as the last member of an organization, leaving the org orphaned. We’ve added explicit guardrails.

• Deleting the last remaining member of an organization or workspace is now blocked, so you can never accidentally leave an org without anyone to administer it.
• Workspaces and organizations can be deactivated and deleted with the new last-member check applied consistently across both actions.
• Downstream services such as billing and data are notified of deactivations so usage and access stop immediately.