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.

web/src/jmap/types.ts

@@ -38,6 +38,8 @@ export interface JmapSession {
     server?: {
       /** "oss" | "community" | "enterprise". Stalwart publishes no version. */
       edition?: string | null;
+      /** Where Stalwart's own administration is (STALWART_ADMIN_URL), for a session that may administer. */
+      adminUrl?: string | null;
     };
     /**
      * False when this session may not administer: the operator turned it off,