fix(qsl): separate the QSL manager from the routing method (#16)

QSL_VIA is the manager. QSL_SENT_VIA and QSL_RCVD_VIA are the ADIF "QSL Via"
enumeration — B bureau, D direct, E electronic, M manager (import-only) —
and say how a card travelled. OpsLog had one column for all three:

  - the import folded QSL_SENT_VIA into QSL_VIA whenever QSL_VIA was empty,
    which is exactly a Log4OM export (it defaults QSL_SENT_VIA to E), so
    OE6CLD saw "E" everywhere OpsLog shows the manager;
  - QSL_RCVD_VIA was listed in adifPromoted with no column behind it, so it
    was not stored, not kept among the extras, and not exported — dropped
    outright on import;
  - neither was ever written on export, so an import followed by an export
    destroyed both;
  - and OpsLog polluted the field itself: the QSL Manager panel wrote
    "Bureau" / "Direct" / "Electronic", in full words, into QSL_VIA.

Two columns added (migration 0027), carried through the five places a
promoted ADIF field has to touch, with round-trip tests pinning the reported
case. The QSL panel now offers Bureau / Direct / Electronic for each
direction and stores the enumeration; the manager field is labelled as the
manager and holds only that. M is kept when a file gives it and never
written back out.

Existing logs hold a mixture of the two in one column. The repair is offered,
not performed: the count is shown once per log with a plain question, and a
"no" is remembered. It moves only where QSL_SENT_VIA is still empty, and only
values that normalise to the enumeration — a manager is a callsign and can
never be one of those six words, which a test pins against real manager calls.

internal/adif/roundtrip_test.go

@@ -119,3 +119,85 @@ func renderRecord(q qso.QSO, includeApp bool) string {
 	bw.Flush()
 	return buf.String()
 }
+
+// TestQSLViaFieldsRoundTrip covers the case reported as issue #16: a log
+// exported by another logger carries a manager in QSL_VIA and a routing method
+// in QSL_SENT_VIA, and the two must stay apart.
+//
+// Before this, QSL_SENT_VIA was folded into QSL_VIA whenever QSL_VIA was empty
+// — so a Log4OM log, which defaults QSL_SENT_VIA to E, showed "E" wherever
+// OpsLog displays the manager — and QSL_RCVD_VIA was thrown away outright: it
+// was listed as a promoted field with no column behind it, so it was not even
+// kept among the extras. Neither was ever exported, which made an import
+// followed by an export destroy both.
+func TestQSLViaFieldsRoundTrip(t *testing.T) {
+	in := qso.QSO{
+		Callsign: "3B9FR", Band: "20m", Mode: "CW",
+		QSODate:    time.Date(2026, 6, 6, 12, 0, 0, 0, time.UTC),
+		QSLVia:     "M0OXO", // the manager
+		QSLSentVia: "D",     // sent direct
+		QSLRcvdVia: "B",     // came back via the bureau
+	}
+	var buf bytes.Buffer
+	bw := bufio.NewWriter(&buf)
+	bw.WriteString("<EOH>\n")
+	writeRecord(bw, in, true, nil)
+	bw.Flush()
+
+	var rec Record
+	if err := Parse(strings.NewReader(buf.String()), func(r Record) error { rec = r; return nil }); err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	out, ok := recordToQSO(rec)
+	if !ok {
+		t.Fatal("recordToQSO returned !ok")
+	}
+	for name, c := range map[string]struct{ got, want string }{
+		"QSL_VIA":      {out.QSLVia, in.QSLVia},
+		"QSL_SENT_VIA": {out.QSLSentVia, in.QSLSentVia},
+		"QSL_RCVD_VIA": {out.QSLRcvdVia, in.QSLRcvdVia},
+	} {
+		if c.got != c.want {
+			t.Errorf("%s: got %q, want %q", name, c.got, c.want)
+		}
+	}
+}
+
+// TestQSLSentViaDoesNotBecomeManager pins the exact shape a Log4OM export has:
+// no QSL_VIA at all, QSL_SENT_VIA defaulted to E. The manager field must come
+// back empty rather than holding "E".
+func TestQSLSentViaDoesNotBecomeManager(t *testing.T) {
+	const rec = "<CALL:5>OE6CLD<QSO_DATE:8>20260606<TIME_ON:4>1200<BAND:3>20m<MODE:2>CW" +
+		"<QSL_SENT_VIA:1>E<EOR>\n"
+	var got Record
+	if err := Parse(strings.NewReader("<EOH>\n"+rec), func(r Record) error { got = r; return nil }); err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	q, ok := recordToQSO(got)
+	if !ok {
+		t.Fatal("recordToQSO returned !ok")
+	}
+	if q.QSLVia != "" {
+		t.Errorf("QSL_VIA = %q — the routing method leaked into the manager field again", q.QSLVia)
+	}
+	if q.QSLSentVia != "E" {
+		t.Errorf("QSL_SENT_VIA = %q, want %q", q.QSLSentVia, "E")
+	}
+}
+
+// M is import-only in the ADIF QSL Via enumeration: keep it when given, never
+// write it back out.
+func TestQSLViaManagerIsImportOnly(t *testing.T) {
+	in := qso.QSO{
+		Callsign: "3B9FR", Band: "20m", Mode: "CW",
+		QSODate:    time.Date(2026, 6, 6, 12, 0, 0, 0, time.UTC),
+		QSLSentVia: "M", QSLRcvdVia: "M",
+	}
+	var buf bytes.Buffer
+	bw := bufio.NewWriter(&buf)
+	writeRecord(bw, in, true, nil)
+	bw.Flush()
+	if s := buf.String(); strings.Contains(s, "QSL_SENT_VIA") || strings.Contains(s, "QSL_RCVD_VIA") {
+		t.Errorf("exported an import-only value:\n%s", s)
+	}
+}