About: name the webmail node and the mail server node

Settings > About shows which webmail node answered (NODE_NAME, else the
container hostname) and which inbuxa node it talks to: the address the
server's name resolves to from the webmail, named by its PTR record. The
server only tells administrators its node name, so the webmail works it
out itself. Fetched from /api/about/nodes on every visit, cached for a
minute server-side, for troubleshooting a cluster.

Fork-only: upstream ihasmail runs one webmail against one server.
4 new strings, translated in all 9 catalogues.

web/src/locales/de.ts

@@ -1740,6 +1740,11 @@ export const catalog: Catalog = {
     "To confirm, type {phrase}": "Zur Bestätigung {phrase} eingeben",
     "Turn off legacy protocols": "Ältere Mailprotokolle ausschalten",
     "Legacy mail protocols are off for your organization. Only {app} and JMAP apps can sign in.": "Ältere Mailprotokolle sind für Ihre Organisation ausgeschaltet. Nur {app} und JMAP-Apps können sich anmelden.",
+    // ── About: webmail and mail server nodes (inbuxa) ──────────────
+    "Webmail node": "Webmail-Knoten",
+    "Mail server node": "Mailserver-Knoten",
+    "{host} does not resolve": "{host} lässt sich nicht auflösen",
+    "unavailable": "nicht verfügbar",
     // ── Spam filter: the language model's opinion (inbuxa) ──────────
     "Language model's opinion": "Einschätzung des Sprachmodells",
     "One of several signals the spam filter weighed": "Eines von mehreren Signalen, die der Spamfilter berücksichtigt hat",