refactor(operator): remove tenant creation (tenants are partner-owned)

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).

apps/operator/server/api/tenants/index.post.ts

@@ -1,6 +0,0 @@
-import { platformApi } from '~~/server/utils/platform-api'
-
-export default defineEventHandler(async (event) => {
-  const body = await readBody(event)
-  return platformApi(event, '/tenants', { method: 'POST', body })
-})