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/qslvia.go

@@ -0,0 +1,53 @@
+package adif
+
+import "strings"
+
+// The ADIF "QSL Via" enumeration, used by QSL_SENT_VIA and QSL_RCVD_VIA. It
+// says how a card travelled, and is a different thing entirely from QSL_VIA,
+// which is the manager's callsign.
+const (
+	QSLViaBureau     = "B"
+	QSLViaDirect     = "D"
+	QSLViaElectronic = "E"
+	// QSLViaManager is import-only in the standard: it may be read from another
+	// logger's file, never written to one. OpsLog keeps it when it arrives so
+	// the operator's own data is not silently altered, and NormaliseQSLVia is
+	// the only place that decides so.
+	QSLViaManager = "M"
+)
+
+// NormaliseQSLVia folds what other loggers and OpsLog's own older versions put
+// in a routing field down to the ADIF enumeration.
+//
+// It accepts the letter, the English word, and the French one — OpsLog wrote
+// "Bureau", "Direct" and "Electronic" in full for a long time, and the QSL
+// Manager panel still shows those words to a French operator. Anything it does
+// not recognise comes back empty rather than being passed through: this feeds
+// an enumerated ADIF field, and inventing a value there breaks the file for
+// every other logger that reads it.
+func NormaliseQSLVia(s string) string {
+	switch strings.ToUpper(strings.TrimSpace(s)) {
+	case "B", "BUREAU", "BURO", "VIA BUREAU":
+		return QSLViaBureau
+	case "D", "DIRECT":
+		return QSLViaDirect
+	case "E", "ELECTRONIC", "ELECTRONIQUE", "ÉLECTRONIQUE", "OQRS":
+		return QSLViaElectronic
+	case "M", "MANAGER":
+		return QSLViaManager
+	}
+	return ""
+}
+
+// IsQSLViaRouting reports whether a QSL_VIA value is in fact a routing method
+// that ended up in the manager field.
+//
+// It exists for one repair: OpsLog's QSL Manager panel wrote "Bureau",
+// "Direct" and "Electronic" into QSL_VIA, and imports folded QSL_SENT_VIA
+// there too, so logs hold a mixture of managers and routing words in one
+// column. A manager is a callsign, never one of these six words, so the test
+// is exact — but it is deliberately narrow: anything else, including a manager
+// whose callsign happens to be unusual, is left alone.
+func IsQSLViaRouting(s string) bool {
+	return NormaliseQSLVia(s) != ""
+}