DELETE /v1/orgs/:slug — soft-delete an organization (Owner only).

The org drops out of every lookup immediately (inaccessible) but its data is kept for a grace window so the account is recoverable, then a background reconciler purges everything. Billing is canceled and running sandboxes are stopped now so we stop charging + consuming compute; both are best-effort and re-ensured by the purge job. confirm must echo the slug (the dashboard's type-to-confirm).