Restore the connection line in the main window title (#136)

* Restore the connection line in the main window title

While online, the title showed the connection manager's diagnostic
"ON4KST session is authenticated and synchronized" instead of the line
the JavaFX window carried: categories, call, name, locator, users online,
stations shown and messages total. The title now builds that line from
the login preferences and the live station and message tables, so it
follows every new station, filter change and message. The diagnostic
stays where it belongs, in the status bar.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Title: typed categories, no empty category, review fixes

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

app-desktop/src/main/i18n/strings_de.properties

@@ -334,6 +334,8 @@ title.connecting=Verbindung zu ON4KST wird aufgebaut…
 title.authenticating=Verbunden – Anmeldung bei ON4KST läuft…
 title.synchronizing=Verbunden – ON4KST-Chatdaten werden abgeglichen…
 title.disconnected=NICHT VERBUNDEN!
+title.online=Verbunden mit: {0} als {1} ({2}) in {3} ({4} Benutzer online, {5} angezeigt), {6} Nachrichten insgesamt.
+title.bothCategories={0} und {1}
 status.noConnection=Keine ON4KST-Verbindung
 status.linkTooltip=ON4KST-Verbindung: {0}\n{1}
 status.linkConnected=🟢 LINK: Verbunden