docs: say that the import option also fills the confirmation statuses

Asked for as a missing feature. It is not missing — the "fill my station fields"
option has stamped the default QSL / LoTW / eQSL / Club Log / HRDLog / QRZ.com
statuses on empty fields since v0.14. What was missing is any mention of it: the
option's description talked only about MY_* fields, so the behaviour was
undiscoverable except by comparing a log before and after.

The description now says it, in both languages, and names why it matters — a
WSJT-X log carries almost no QSL fields.

The rule is also pinned by a test now, which meant splitting the fill from the
settings lookup: blanks are filled, existing values are never touched.
Overwriting them would erase confirmations the operator has actually received,
and that is the half a future edit is most likely to get wrong.

app.go

@@ -8734,36 +8734,33 @@ func (a *App) applyQSLDefaults(q *qso.QSO) {
 	if err != nil {
 		return
 	}
-	if q.QSLSent == "" {
-		q.QSLSent = d.QSLSent
-	}
-	if q.QSLRcvd == "" {
-		q.QSLRcvd = d.QSLRcvd
-	}
-	if q.LOTWSent == "" {
-		q.LOTWSent = d.LOTWSent
-	}
-	if q.LOTWRcvd == "" {
-		q.LOTWRcvd = d.LOTWRcvd
-	}
-	if q.EQSLSent == "" {
-		q.EQSLSent = d.EQSLSent
-	}
-	if q.EQSLRcvd == "" {
-		q.EQSLRcvd = d.EQSLRcvd
-	}
-	if q.ClublogUploadStatus == "" {
-		q.ClublogUploadStatus = d.ClublogStatus
-	}
-	if q.HRDLogUploadStatus == "" {
-		q.HRDLogUploadStatus = d.HRDLogStatus
-	}
-	if q.QRZComUploadStatus == "" {
-		q.QRZComUploadStatus = d.QRZComStatus
-	}
-	if q.QRZComDownloadStatus == "" {
-		q.QRZComDownloadStatus = d.QRZComCfm
+	applyQSLDefaultsTo(q, d)
+}
+
+// applyQSLDefaultsTo stamps the operator's default confirmation statuses on the
+// fields a QSO leaves EMPTY. Split from the settings lookup so the rule can be
+// tested: fill the blanks, never touch a value that is already there.
+//
+// The distinction matters on import. A WSJT-X log carries almost no QSL fields,
+// so without this every imported QSO would sit with blank statuses; a log
+// exported from another program carries real ones, and overwriting those would
+// erase confirmations the operator has actually received.
+func applyQSLDefaultsTo(q *qso.QSO, d QSLDefaults) {
+	fill := func(dst *string, def string) {
+		if *dst == "" {
+			*dst = def
+		}
 	}
+	fill(&q.QSLSent, d.QSLSent)
+	fill(&q.QSLRcvd, d.QSLRcvd)
+	fill(&q.LOTWSent, d.LOTWSent)
+	fill(&q.LOTWRcvd, d.LOTWRcvd)
+	fill(&q.EQSLSent, d.EQSLSent)
+	fill(&q.EQSLRcvd, d.EQSLRcvd)
+	fill(&q.ClublogUploadStatus, d.ClublogStatus)
+	fill(&q.HRDLogUploadStatus, d.HRDLogStatus)
+	fill(&q.QRZComUploadStatus, d.QRZComStatus)
+	fill(&q.QRZComDownloadStatus, d.QRZComCfm)
 }
 
 // ── External services (logbook upload) ─────────────────────────────────