Add Tenants to Administration, and let an account be put in one

A tenant is a separate organisation on one server: its own people,
domains and limits, and an administrator who manages only what is in it.
It gets a section under Access, gated by sysTenantQuery and sysTenantGet,
with a notice on a server that does not report Enterprise, where anyone
inside a tenant is held to an ordinary user's permissions.

The panel edits the tenant's name, logo, role and limits. The logo is an
https address, drawn through the image proxy the strict image policy
requires, or an image data URL. Limits change one quotas/<name> pointer
each, so the four ihasmail does not offer keep their values, and an empty
field is no limit. The role is the most anyone inside can be allowed.

Stalwart keeps no list on a tenant -- each account, group, domain, list and
role names its own -- so what a tenant holds is counted with memberTenantId
queries and shown against its limits. Domains are added and taken out from
the tenant's panel, one memberTenantId change each; only a domain in no
tenant can be added, and its accounts stay where they are. Delete is offered
once every count reads zero.

A tenant does nothing until someone administers it, so the account panel
gains a Tenant choice for an administrator who can read tenants: an
Administrator inside a tenant administers that tenant. Nobody moves their
own account.

The mock has a tenant holding a domain and an administrator, a spare domain
to assign, memberTenantId filters on every query, and Stalwart's rule that
only an administrator outside every tenant may move things into one. A test
of taking a domain back out found that the mock's pointer handling dropped a
top-level null instead of storing it, so nothing had ever been cleared that
way; it stores null now, as the server reads it back.

Nothing about tenants has been written on a live server: production has
none. KNOWN-ISSUES says what was read from source.

Thirty-nine new strings and one plural, in all nine catalogues.

web/src/views/admin/AccountSheet.tsx

@@ -85,6 +85,7 @@ export function AccountSheet({ account, ctx, onClose, onChanged, onCreated, onDe
   const [role, setRole] = useState(roleKey(account?.roles));
   const [quota, setQuota] = useState(gibOf(account?.quotas?.[DISK_QUOTA]));
   const [aliases, setAliases] = useState<EmailAlias[]>(() => Object.values(account?.aliases ?? {}));
+  const [tenantId, setTenantId] = useState(account?.memberTenantId ?? "");
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
 
@@ -132,7 +133,7 @@ export function AccountSheet({ account, ctx, onClose, onChanged, onCreated, onDe
           setError(t("An account needs an address."));
           return;
         }
-        const id = await createAccount({ name, domainId, description, password, roles: rolesFromKey(role), diskQuotaBytes: bytesOf(quota) });
+        const id = await createAccount({ name, domainId, description, password, roles: rolesFromKey(role), diskQuotaBytes: bytesOf(quota), memberTenantId: tenantId || null });
         toast.success(t("Created {address}", { address }));
         onCreated(id);
         return;
@@ -140,6 +141,7 @@ export function AccountSheet({ account, ctx, onClose, onChanged, onCreated, onDe
       const patch: Record<string, unknown> = {};
       if ((account.description ?? "") !== description) patch.description = description.trim() || null;
       if (roleKey(account.roles) !== role) patch.roles = rolesFromKey(role);
+      if ((account.memberTenantId ?? "") !== tenantId) patch.memberTenantId = tenantId || null;
       if ((account.quotas?.[DISK_QUOTA] ?? null) !== bytesOf(quota)) patch.quotas = quotasWithDisk(account.quotas, bytesOf(quota));
       const before = JSON.stringify(aliasList(Object.values(account.aliases ?? {})));
       if (before !== JSON.stringify(aliasList(aliases))) patch.aliases = aliasList(aliases);
@@ -245,6 +247,18 @@ export function AccountSheet({ account, ctx, onClose, onChanged, onCreated, onDe
           {self ? t("You can't change your own role.") : t("Only roles whose permissions you hold yourself are offered. On an account inside a tenant, Administrator means administrator of that tenant.")}
         </p>
 
+        {ctx.tenants && (ctx.tenants.length > 0 || tenantId) && (
+          <>
+            <h3>{t("Tenant")}</h3>
+            <select className="input admin-wide" aria-label={t("Tenant")} value={tenantId} disabled={!editable || self} onChange={(e) => setTenantId(e.target.value)}>
+              <option value="">{t("No tenant")}</option>
+              {ctx.tenants.map((x) => <option key={x.id} value={x.id}>{x.name}</option>)}
+              {tenantId && !ctx.tenants.some((x) => x.id === tenantId) && <option value={tenantId}>{tenantId}</option>}
+            </select>
+            <p className="hint">{self ? t("You can't move your own account into a tenant.") : t("An account in a tenant is limited by the tenant's role and counts towards its limits, and Administrator means administrator of that tenant.")}</p>
+          </>
+        )}
+
         <h3>{t("Storage")}</h3>
         {!creating && (
           <p className="hint" style={{ marginTop: 0 }}>