Follow what the live server does with tenants and domains

A run on the production server with throwaway tenants, a role, lists and a
domain, all removed, found three things the source reading had not:

- Something in a tenant has to be on a domain in that tenant (a list in a
  tenant on an unassigned domain is invalidForeignKey), while something in
  no tenant may be on a tenant's domain. The account panel's tenant choice
  offered every tenant; it offers only the domain's now, and a new account
  starts in the tenant of the domain it is made on. The domain list reads
  memberTenantId for it.
- A domain created in a tenant puts its DKIM keys there too, and they keep
  the tenant from being deleted. They are counted with the rest, so Delete
  is not offered while any remain.
- Stalwart lets a domain leave a tenant while the tenant still has accounts
  on it, stranding them. The panel asks first and refuses while any are
  there.

The refusal to delete a tenant that holds anything was confirmed, as were
tenant create, quota pointers, logo and rename. The mock follows the domain
rule, filters DKIM keys by tenant, and KNOWN-ISSUES records the run.

The non-Enterprise notice is now just "Tenants are a Stalwart Enterprise
feature." Two sentences were reworded and one plural added, in all nine
catalogues, and the old sentences are gone.

web/src/views/admin/__tests__/tenant-sheet.test.tsx

@@ -8,7 +8,8 @@ import type { DirectoryTenant } from "@/lib/adminTenants";
 (globalThis as { IS_REACT_ACT_ENVIRONMENT?: boolean }).IS_REACT_ACT_ENVIRONMENT = true;
 
 const api = vi.hoisted(() => ({
-  counts: { accounts: 1, groups: 0, lists: 0, domains: 1, roles: 0 } as Record<string, number>,
+  counts: { accounts: 1, groups: 0, lists: 0, domains: 1, roles: 0, dkimKeys: 2 } as Record<string, number>,
+  onDomain: 0,
   updateTenant: vi.fn(async () => {}),
   setDomainTenant: vi.fn(async () => {}),
 }));
@@ -18,6 +19,7 @@ vi.mock("@/lib/adminTenants", async (original) => ({
   tenantDomains: vi.fn(async () => ({ inTenant: [{ id: "d3", name: "old-brand.example" }], unassigned: [{ id: "d4", name: "spare.example" }] })),
   updateTenant: api.updateTenant,
   setDomainTenant: api.setDomainTenant,
+  tenantAccountsOnDomain: vi.fn(async () => api.onDomain),
 }));
 
 const { TenantSheet } = await import("../TenantSheet");
@@ -49,7 +51,8 @@ describe("the tenant sheet", () => {
     root = createRoot(host);
     api.updateTenant.mockClear();
     api.setDomainTenant.mockClear();
-    api.counts = { accounts: 1, groups: 0, lists: 0, domains: 1, roles: 0 };
+    api.counts = { accounts: 1, groups: 0, lists: 0, domains: 1, roles: 0, dkimKeys: 2 };
+    api.onDomain = 0;
   });
   afterEach(async () => {
     await act(async () => root.unmount());
@@ -64,7 +67,7 @@ describe("the tenant sheet", () => {
   });
 
   it("offers the delete once it is empty", async () => {
-    api.counts = { accounts: 0, groups: 0, lists: 0, domains: 0, roles: 0 };
+    api.counts = { accounts: 0, groups: 0, lists: 0, domains: 0, roles: 0, dkimKeys: 0 };
     signIn(ALL);
     await render();
     expect(button(host, "Delete tenant…")?.disabled).toBe(false);
@@ -92,3 +95,30 @@ describe("the tenant sheet", () => {
     expect(button(host, "Take old-brand.example out of the tenant")).toBeUndefined();
   });
 });
+
+describe("taking a domain out of a tenant", () => {
+  let host: HTMLDivElement;
+  let root: Root;
+  beforeEach(() => {
+    host = document.createElement("div");
+    document.body.appendChild(host);
+    root = createRoot(host);
+    api.setDomainTenant.mockClear();
+  });
+  afterEach(async () => {
+    await act(async () => root.unmount());
+    host.remove();
+  });
+
+  it("is refused while the tenant still has accounts on it, which Stalwart would strand", async () => {
+    api.onDomain = 2;
+    signIn(ALL);
+    await act(async () => {
+      root.render(<TenantSheet tenant={tenant} roles={new Map()} onClose={() => {}} onChanged={() => {}} onCreated={() => {}} onDeleted={() => {}} />);
+    });
+    await act(async () => {});
+    await act(async () => button(host, "Take old-brand.example out of the tenant")!.click());
+    expect(api.setDomainTenant).not.toHaveBeenCalled();
+    expect(host.querySelector(".admin-notice.error")?.textContent).toContain("2 accounts in this tenant are still on old-brand.example");
+  });
+});