Add the edit contact dialog

Ctrl+Y from the entry window, or Enter on a row in the log, opens the whole
contact in one dialog. It reaches the fields the log has no column for: QSX
frequency, name, QTH, comment, grid, power, radio number, run position, and the
country and WPX prefixes. Previous and Next walk the log without closing and
offer to save first.

The dialog checks values through the same QsoEditor the log columns use, so a
zone the contest will not take is refused the same way in both places.
QsoEdit now names the field that was refused, so the dialog can put the cursor
back in the right box, and QsoEditor.ApplyAll changes several fields at once.

Points and the multiplier flags are shown but not editable. They are worked out
from the rules every time the log changes, so a typed value would be lost on
the next edit. N1MM lets you type them; we do not, rather than offering a box
that does nothing.

A contact's own country prefix now wins over the country file when scoring.
Without this, correcting the country in the dialog would change what the log
shows and what Cabrillo says, but not the score.

LoggingSession.Update now broadcasts the change like Edit does, so a contact
saved from the dialog reaches the other stations.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

README.md

@@ -45,7 +45,7 @@ scorer: red for a dupe, green for a new multiplier, blue for points.
 | Log | N1MM `.s3db`, Cabrillo 3.0 out, ADIF in and out |
 | While typing | dupe check, multiplier check, points, country and zone from the country file |
 | Windows | entry, log, check, bandmap, score summary, packet |
-| Editing | double-click a cell in the log to change it, Delete to remove the contact; both go out to the other stations |
+| Editing | double-click a cell in the log, or open the whole contact with Ctrl+Y; Delete removes it. All of it goes out to the other stations |
 | Radio | hamlib `rigctld`, reconnecting on its own |
 | Cluster | DX cluster over telnet, spots feeding the bandmap |
 | Network | contacts shared with the other stations of a multi-operator entry, in N1MM's own contact message |
@@ -107,6 +107,18 @@ Delete, or the right-click menu, removes the selected contact after a
 confirmation. Either way the whole log is scored again, so a multiplier the
 removed contact was holding passes to the next contact that claims it.
 
+**Edit → Edit Last Contact**, Ctrl+Y, or Enter on a row in the log opens the
+whole contact in one dialog. That is where the fields with no log column live:
+QSX frequency, name, QTH, comment, grid, power, radio number, run position, and
+the country and WPX prefixes. ◀ and ▶ walk the log without closing, offering to
+save first. Points and the multiplier flags are shown but cannot be typed in —
+they are worked out from the rules every time the log changes, so anything typed
+there would be overwritten on the next edit.
+
+Correcting the country prefix by hand changes the score. The country file is a
+best guess for calls it has no rule for, so what the contact says now wins over
+what the file says.
+
 ### Networked stations
 
 **Config → Network** names this station and lists the others. Each contact is