Point from the dashboard to Stalwart's own administration

A line under the cards says where the rest is: detailed metrics, the
delivery queue, logs and server settings are in Stalwart's own
administration. It links there when the operator sets STALWART_ADMIN_URL,
and stays plain text otherwise, because STALWART_URL is how this server
reaches Stalwart and is often an address no browser can open.

Several servers: a servers file entry may now be an object,
{"url": ..., "adminUrl": ...}, and a session routed to that server gets its
adminUrl. A routed domain without one gets no link rather than the default
server's, for the same reason routing never falls back. The URL is sent
only to a session that may administer.

The shipped example file stopped the server at startup: its "_comment"
key was read as a domain and refused as not a URL, while the test that
checks the example skipped it. Keys starting with an underscore are notes
now -- no mail domain starts with one -- and the example is also loaded
through the real parser in a test, so the two cannot disagree again.

Two new strings, in all nine catalogues.

server/src/app.ts

@@ -23,6 +23,7 @@ import {
   getAccountInfo,
   getUpstreamSession,
   upstreamFor,
+  adminUrlFor,
   localizeSession,
 } from "./upstream.js";
 import {
@@ -865,8 +866,12 @@ function sessionExtras(session: LiveSession, info: AccountInfo = { locale: null,
       remember: session.remember,
       /** Locale configured for the account in Stalwart's directory, if readable. */
       userLocale: info.locale,
-      /** What the upstream server would tell us about itself. */
-      server: { edition: info.edition },
+      /**
+       * What the upstream server would tell us about itself, and -- for a
+       * session that may administer -- where the operator says its own
+       * administration is.
+       */
+      server: { edition: info.edition, adminUrl: administrationAllowed(config.administration, session.remember) ? adminUrlFor(session.username) : null },
       /**
        * Whether this session may administer: the installation offers it
        * (ADMINISTRATION) and the person signed in on a device marked as their own.