Mark the CQ frequency on the bandmap and leave Run when the radio moves off it

Starting Run stores the frequency in the position. The bandmap draws a
purple, bold "CQ Frequency" pseudospot there, which is not added to the
shared bandmap, and a click on it tunes back and sets Run. A move of more
than 3 kHz (a setting on the telnet Filters tab) while running switches
to search and pounce.

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

src/Nonemm.Session/OperatingPosition.cs

@@ -46,7 +46,28 @@ public sealed class OperatingPosition
 
     /// True while the operator is calling CQ on this radio rather than
     /// searching. Each radio runs or searches on its own.
-    public bool IsRunning { get; set; }
+    public bool IsRunning
+    {
+        get => running;
+        set
+        {
+            if (value && !running)
+            {
+                CqFrequency = Frequency;
+            }
+            running = value;
+        }
+    }
+
+    private bool running;
+
+    /// Where this radio last started running or sent a CQ. It stays after the
+    /// radio goes back to searching, so the operator can return to it.
+    public Frequency? CqFrequency { get; set; }
+
+    /// How far, in hertz, the radio can move off the CQ frequency before the
+    /// position goes back to searching.
+    public long CqLeaveHertz { get; set; } = 3_000;
 
     /// The other operator's name and a note about the contact. Neither is part
     /// of any exchange: the name is what a contact being quick edited already
@@ -110,6 +131,10 @@ public sealed class OperatingPosition
             FillSentExchange();
         }
         TransmitFrequency = transmitFrequency ?? TransmitFrequency;
+        if (running && CqFrequency is { } cq && Math.Abs(frequency.Hertz - cq.Hertz) > CqLeaveHertz)
+        {
+            running = false;
+        }
         Session.NotifyChanged();
     }