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/fields.go

@@ -135,8 +135,8 @@ var Fields = []FieldDef{
 	{Name: "QSLSDATE", Kind: KindDate, Category: "QSL", Promoted: true},
 	{Name: "QSLRDATE", Kind: KindDate, Category: "QSL", Promoted: true},
 	{Name: "QSL_VIA", Kind: KindText, Category: "QSL", Promoted: true},
-	{Name: "QSL_SENT_VIA", Kind: KindEnum, Category: "QSL"},
-	{Name: "QSL_RCVD_VIA", Kind: KindEnum, Category: "QSL"},
+	{Name: "QSL_SENT_VIA", Kind: KindEnum, Category: "QSL", Promoted: true},
+	{Name: "QSL_RCVD_VIA", Kind: KindEnum, Category: "QSL", Promoted: true},
 	{Name: "QSLMSG", Kind: KindText, Category: "QSL", Promoted: true},
 	{Name: "QSLMSG_INTL", Kind: KindText, Category: "QSL", Intl: true},
 	{Name: "QSLMSG_RCVD", Kind: KindText, Category: "QSL", Promoted: true},