AGPL source offer and name cleanup

Every build writes the exact source it was built from, uncommitted work and
new files included, as source.tar.gz next to the app, named after that tree.
Docker builds, which have no git, pack the build context and name it by a
hash of its files. The sign-in page and Settings > About link to it instead of
a repository that can drift.

What users, operators and packagers see no longer names the upstream server:
- interface text, in all nine catalogues, with a token-session line for
  Security;
- server messages;
- the settings, now MAIL_SERVER_URL, MAIL_SERVERS_FILE, ADMIN_URL and
  MAIL_SERVER_FOLLOW_ADVERTISED_URLS, and mail-servers.example.json;
- the Tenants notice, which is gone;
- the README, CONTRIBUTING and SECURITY.

ihasmail's own FEATURES, KNOWN-ISSUES and ROADMAP stay with public ihasmail,
and INBUXA.md is folded into the README.

web/src/views/admin/TenantsAdmin.tsx

@@ -7,7 +7,6 @@ import { drawableLogo, getTenants, queryTenants, type DirectoryTenant } from "@/
 import { formatSize } from "@/lib/format";
 import { proxiedImageUrl } from "@/lib/text/html";
 import { plural, t } from "@/lib/i18n";
-import { useSession } from "@/store/session";
 import { Empty, Spinner } from "@/ui/misc";
 import { usePermissions } from "./usePermissions";
 import { TenantSheet } from "./TenantSheet";
@@ -18,23 +17,15 @@ const PAGE_SIZE = 50;
  * Tenants: separate organizations on one server, each with its own people,
  * domains and limits.
  *
- * The section is offered to whoever may read tenants. INBUXA ships tenants to
- * everybody, whatever edition the server reports, so there is no edition
- * check here (public ihasmail shows only a notice unless the server reports
- * Enterprise). SHOW_ENTERPRISE_NOTICES still adds the notice, for talking to
- * upstream Stalwart.
+ * The section is offered to whoever may read tenants. The INBUXA mail server
+ * has one edition with tenants in it, so there is no edition check and no
+ * notice here, unlike public ihasmail.
  */
 export function TenantsAdmin({ selectedId }: { selectedId?: string }) {
-  const notices = useSession((s) => s.session?.ihasmail?.server?.enterpriseNotices === true);
-  return <EnterpriseTenants selectedId={selectedId} notice={notices} />;
+  return <EnterpriseTenants selectedId={selectedId} />;
 }
 
-/** Said on every Tenants page, Enterprise or not. */
-function EnterpriseNotice({ warn }: { warn: boolean }) {
-  return <p className={`admin-notice${warn ? " warn" : ""}`}>{t("Tenants are a Stalwart Enterprise feature.")}</p>;
-}
-
-function EnterpriseTenants({ selectedId, notice }: { selectedId?: string; notice: boolean }) {
+function EnterpriseTenants({ selectedId }: { selectedId?: string }) {
   const [, navigate] = useLocation();
   const perms = usePermissions();
   const [text, setText] = useState("");
@@ -111,7 +102,6 @@ function EnterpriseTenants({ selectedId, notice }: { selectedId?: string; notice
         )}
       </div>
 
-      {notice && <EnterpriseNotice warn={false} />}
 
       <div className="admin-toolbar">
         <label className="admin-search">