Keep an operator's windows, colours and recordings

Ctrl+O asks who is at the radio, as it does in N1MM, and the callsign goes on
every contact logged from then on. A multi-operator station changes hands every
few hours, so each operator also keeps what he wants the program to look like:
where the windows sit, the theme, and the folder his recordings are in.

The windows on the screen are stored against the operator leaving, before the
dialog opens, and the operator taking over gets his own back. A window he opens
later is placed as it appears. An operator who is new to the list starts with
whatever is on the screen.

Nothing plays the recordings yet, so the folder is stored and waits on voice
keying. {OPERATOR} in a message sends the callsign.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RoGtneMQaz4M9w7Kk49AVD

src/Nonemm.App/Configuration/Settings.cs

@@ -186,6 +186,14 @@ public sealed record Settings
 
     public IReadOnlyList<string> PhoneMessages { get; init; } = [];
 
+    /// The operators at this station, and their windows and colours. N1MM
+    /// keeps an operator's callsign against every contact he logs; this keeps
+    /// what he wants the program to look like as well.
+    public IReadOnlyList<StoredOperator> Operators { get; init; } = [];
+
+    /// Whoever is at the radio now, or empty at a station with one operator.
+    public string CurrentOperator { get; init; } = "";
+
     /// The digital window's twenty-four macro buttons, in the same
     /// `label,message` lines as a function key file. Empty means the built-in
     /// set.