feat(lookup): optional QRZ nickname as the logged name

QRZ publishes <nickname> — the name an operator goes BY on the air — and
OpsLog was composing fname + name instead. "Bob" is what belongs in a log;
"Robert J Smith" is what belongs on a licence.

QRZ only, and deliberately so: HamQTH's <nick> already fills the Name field
that way, so the same switch there would toggle a behaviour it has no way to
turn off.

A published nickname is optional, so an empty one falls through to the
registered name. That is the whole point of it being a fallback rather than a
swap, and it is what the test pins — a blank nickname must never blank the
name.

internal/lookup/qrz.go

@@ -21,8 +21,14 @@ type QRZ struct {
 
 	HTTP *http.Client
 
-	mu      sync.Mutex
-	session string
+	// PreferNickname takes QRZ's <nickname> over the composed first+last name
+	// when the operator has published one. It is the name they go BY on the air,
+	// which is what belongs in a log — HamQTH's <nick> is already used that way,
+	// and this brings QRZ into line for operators who want it.
+	PreferNickname bool
+
+	mu       sync.Mutex
+	session  string
 	loggedAt time.Time
 }
 
@@ -117,7 +123,7 @@ func (q *QRZ) fetch(ctx context.Context, sessionKey, callsign string) (Result, e
 	}
 	r := Result{
 		Callsign:  strings.ToUpper(c.Call),
-		Name:      joinName(c.FName, c.Name),
+		Name:      qrzName(q.PreferNickname, c.Nickname, c.FName, c.Name),
 		QTH:       c.Addr2,
 		Address:   composeQRZAddress(c.Addr1, c.Addr2, c.Zip, c.Country),
 		State:     strings.ToUpper(c.State),
@@ -169,6 +175,7 @@ type qrzSession struct {
 type qrzCallsign struct {
 	Call      string `xml:"call"`
 	FName     string `xml:"fname"`
+	Nickname  string `xml:"nickname"` // the name the operator goes by on the air
 	Name      string `xml:"name"`
 	Addr1     string `xml:"addr1"`
 	Addr2     string `xml:"addr2"`
@@ -235,3 +242,17 @@ func firstNonEmpty(s ...string) string {
 	}
 	return ""
 }
+
+// qrzName picks what goes in the log's Name field.
+//
+// The nickname is only taken when the operator asked for it AND QRZ has one —
+// a blank nickname must never blank the name, which is the whole reason this is
+// a fallback rather than a swap.
+func qrzName(preferNickname bool, nickname, fname, name string) string {
+	if preferNickname {
+		if n := strings.TrimSpace(nickname); n != "" {
+			return n
+		}
+	}
+	return joinName(fname, name)
+}