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/pages/tenants/index.vue

@@ -7,16 +7,6 @@ const { data: tenants, refresh, pending } = await useFetch<Tenant[]>('/api/tenan
 
 const search = ref('')
 const statusFilter = ref<'all' | TenantStatus>('all')
-const createOpen = ref(false)
-
-async function onCreated(tenant: Tenant) {
-  createOpen.value = false
-  // Refresh the list so the new row appears immediately, then jump into the
-  // detail page — that's where the operator will configure domains, billing,
-  // and trigger provisioning.
-  await refresh()
-  await navigateTo(`/tenants/${tenant.slug}`)
-}
 
 const filtered = computed(() => {
   const q = search.value.trim().toLowerCase()
@@ -60,15 +50,9 @@ function navTo(t: Tenant) {
           <template #leading><UiIcon name="refresh" :size="13" /></template>
           Refresh
         </UiButton>
-        <UiButton variant="primary" @click="createOpen = true">
-          <template #leading><UiIcon name="plus" :size="13" /></template>
-          New tenant
-        </UiButton>
       </template>
     </PageHeader>
 
-    <NewTenantModal :open="createOpen" @close="createOpen = false" @created="onCreated" />
-
     <div class="stage">
       <div class="filters">
         <div class="search">