Give each operator his windows back

The program stored an operator's window positions but never used them at
startup: the entry window was not placed and no window was reopened. It
now restores the whole screen both at startup and on a change of
operator: the windows that operator had open, where he had them, and the
ones he did not have closed.

The second radio's entry window no longer saves the layout. It has none
of the other windows open, so saving from it dropped every window the
first one had.

Ctrl+O gets six buttons for the operators last at the radio, newest
first. One click changes to that operator.

The recordings folder is no longer asked for. It is `Wav/<callsign>`
under the data folder, which is where N1MM plays them from, so
`StoredOperator.WavPath` is gone.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0157i7PiZyqBkquxS9A6FTdQ

src/Nonemm.App/Configuration/Settings.cs

@@ -253,6 +253,12 @@ public sealed record Settings
     /// Whoever is at the radio now, or empty at a station with one operator.
     public string CurrentOperator { get; init; } = "";
 
+    /// The operators who were last at the radio, newest first. `Operators` is
+    /// kept in the order they took it, so the end of the list is the most
+    /// recent.
+    public IEnumerable<StoredOperator> RecentOperators(int count) =>
+        Operators.Reverse().Take(count);
+
     /// 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.