feat: serial CW keyer — add invert (active-LOW) polarity option

Some CW interfaces key on the opposite line level (transmit at rest / key
backwards). New "Invert keying (active-LOW)" toggle flips the asserted level for
both the CW and PTT lines, and the idle state drives both lines to their
inactive level accordingly so an active-low rig isn't left keyed at rest.
Default off = N1MM convention (line HIGH = active).

app.go

@@ -218,6 +218,7 @@ const (
 	keyWKEscClears  = "winkeyer.esc_clears_call" // ESC also clears the callsign
 	keyWKSendOnType = "winkeyer.send_on_type"    // key characters live as typed
 	keyWKCWLine     = "winkeyer.cw_key_line"     // serial engine: "dtr" (CW) / "rts" (PTT) or swapped
+	keyWKCWInvert   = "winkeyer.cw_invert"       // serial engine: invert line polarity (active-LOW)
 
 	keyClusterAutoConnect = "cluster.auto_connect" // open every enabled server at app start
 
@@ -13053,7 +13054,7 @@ func (a *App) GetWinkeyerSettings() (WinkeyerSettings, error) {
 		keyWKEnabled, keyWKPort, keyWKBaud, keyWKWPM, keyWKWeight, keyWKLeadIn,
 		keyWKTail, keyWKRatio, keyWKFarnsworth, keyWKSidetone, keyWKMode,
 		keyWKSwap, keyWKAutoSpace, keyWKUsePTT, keyWKSerialEcho, keyWKMacros,
-		keyWKEngine, keyWKEscClears, keyWKSendOnType, keyWKCWLine)
+		keyWKEngine, keyWKEscClears, keyWKSendOnType, keyWKCWLine, keyWKCWInvert)
 	if err != nil {
 		return out, err
 	}
@@ -13063,6 +13064,7 @@ func (a *App) GetWinkeyerSettings() (WinkeyerSettings, error) {
 	if v := m[keyWKCWLine]; v != "" {
 		out.CWKeyLine = v
 	}
+	out.CWInvert = m[keyWKCWInvert] == "1"
 	if v := m[keyWKEscClears]; v != "" {
 		out.EscClearsCall = v == "1"
 	}
@@ -13130,6 +13132,7 @@ func (a *App) SaveWinkeyerSettings(s WinkeyerSettings) error {
 		keyWKEscClears:  boolStr(s.EscClearsCall),
 		keyWKSendOnType: boolStr(s.SendOnType),
 		keyWKCWLine:     strings.TrimSpace(s.CWKeyLine),
+		keyWKCWInvert:   boolStr(s.CWInvert),
 	} {
 		if err := a.settings.Set(a.ctx, k, v); err != nil {
 			return err