The operator could list and inspect tenants but had no create flow — tenant
creation only existed as the partner-portal wizard, which always attaches a
partnerId. Platform-api's POST /tenants (platform-admin only, no partner
field) was already built for this; add the missing UI: a New tenant modal on
the tenants page (slug, name, plan/cycle/currency/seats, optional primary
mail domain + first-admin invite) and the server proxy route. Operator-created
tenants are direct customers; attach a partner later if needed.
Tenants always belong to a partner, so the operator must not create orphan (partnerless) tenants. Remove the NewTenantModal component, the POST /api/tenants proxy route, and the New-tenant button/modal from the tenants page. Tenant creation now happens only via the partner portal wizard (which forces partnerId).
Wires the previously-dead 'New tenant' button on /tenants to a modal
that collects slug + name + plan + optional primary domain, POSTs to
the existing platform-api /tenants endpoint via a new operator proxy,
and navigates into the freshly-created tenant detail page. Slug
auto-derives from the name until the operator types in the slug field
themselves. Billing details and provisioning are still done from the
tenant detail page after creation — this modal is the minimum that
backend validators will accept.