feat(rotator): add Hy-Gain DCU-1 backend (RotorCard DXA, Rotor-EZ, Green Heron)

New internal/rotator/dcu1 client speaking the DCU-1 command set (AP1nnn / AM1
to go-to, AI1 to read bearing), over a serial COM port (4800 baud default) or a
raw TCP serial-over-IP bridge. Azimuth-only; Stop re-commands the current
bearing since the base set has no stop opcode.

Wired through app.go (normRotorType, default port 4001, GoTo/Heading/Stop/test
switches, park returns the same "PstRotator only" note as ARCO) and exposed in
the rotor settings as "Hy-Gain DCU-1 (RotorCard DXA, Rotor-EZ, Green Heron)"
with the ARCO's serial/TCP transport chooser and a bilingual hint. Protocol is
implemented from the standard DCU-1 spec and still needs field confirmation
against a real RotorCard DXA.

app.go

@@ -52,6 +52,7 @@ import (
 	"hamlog/internal/qso"
 	"hamlog/internal/relaydev"
 	"hamlog/internal/rigctld"
+	"hamlog/internal/rotator/dcu1"
 	"hamlog/internal/rotator/gs232"
 	"hamlog/internal/rotator/pst"
 	"hamlog/internal/rotgenius"
@@ -13477,7 +13478,7 @@ type logicalRotor struct {
 
 // normRotorType clamps a rotor type to a known backend.
 func normRotorType(t string) string {
-	if t == "rotgenius" || t == "arco" {
+	if t == "rotgenius" || t == "arco" || t == "dcu1" {
 		return t
 	}
 	return "pst"
@@ -13490,6 +13491,8 @@ func rotatorDefaultPort(typ string) int {
 		return 9006 // 4O3A native default
 	case "arco":
 		return 4001 // placeholder — the real number is set in ARCO's LAN menu
+	case "dcu1":
+		return 4001 // only used with a serial-over-IP bridge; DCU-1 has no standard
 	default:
 		return 12000 // PstRotator UDP
 	}
@@ -13682,6 +13685,16 @@ func arcoClient(l rotorLink) *gs232.Client {
 	return gs232.New(l.Host, l.Port)
 }
 
+// dcu1Client builds the Hy-Gain DCU-1 client for a rotor's transport: the
+// controller's COM port (the usual case — RotorCard DXA, Green Heron, Rotor-EZ)
+// or a serial-over-IP bridge on TCP.
+func dcu1Client(l rotorLink) *dcu1.Client {
+	if l.Transport == "serial" {
+		return dcu1.NewSerial(l.ComPort, l.Baud)
+	}
+	return dcu1.New(l.Host, l.Port)
+}
+
 // RotatorHeading is the live antenna heading for the status bar and compass.
 type RotatorHeading struct {
 	Enabled bool   `json:"enabled"`
@@ -13748,6 +13761,16 @@ func (a *App) GetRotatorHeading() RotatorHeading {
 		base.Azimuth = az
 		base.Raw = raw
 		return base
+	case "dcu1":
+		az, raw, herr := dcu1Client(link).Heading()
+		if herr != nil {
+			base.Raw = herr.Error()
+			return base
+		}
+		base.OK = true
+		base.Azimuth = az
+		base.Raw = raw
+		return base
 	default:
 		az, raw, herr := pst.New(link.Host, link.Port).Heading()
 		if herr != nil {
@@ -13774,6 +13797,8 @@ func (a *App) RotatorGoTo(az int, el int) error {
 		return rotgenius.New(link.Host, link.Port).GoTo(link.Num, az)
 	case "arco":
 		return arcoClient(link).GoTo(az)
+	case "dcu1":
+		return dcu1Client(link).GoTo(az)
 	default:
 		return pst.New(link.Host, link.Port).GoTo(az, link.HasElevation, el)
 	}
@@ -13791,6 +13816,8 @@ func (a *App) RotatorStop() error {
 		return rotgenius.New(link.Host, link.Port).Stop()
 	case "arco":
 		return arcoClient(link).Stop()
+	case "dcu1":
+		return dcu1Client(link).Stop()
 	default:
 		return pst.New(link.Host, link.Port).Stop()
 	}
@@ -13809,6 +13836,8 @@ func (a *App) RotatorPark() error {
 		return fmt.Errorf("park is a PstRotator feature; not available on the Rotator Genius")
 	case "arco":
 		return fmt.Errorf("park is a PstRotator feature; not available over the ARCO GS-232 link")
+	case "dcu1":
+		return fmt.Errorf("park is a PstRotator feature; not available over the DCU-1 link")
 	default:
 		return pst.New(link.Host, link.Port).Park()
 	}
@@ -13847,6 +13876,14 @@ func testRotorLink(l rotorLink) error {
 		// GS-232 — without moving the antenna.
 		_, _, err := arcoClient(l).Heading()
 		return err
+	case "dcu1":
+		if l.Transport == "serial" && strings.TrimSpace(l.ComPort) == "" {
+			return fmt.Errorf("select the DCU-1 controller's COM port first")
+		}
+		// A bearing query (AI1) proves the link and the DCU-1 command set without
+		// moving the antenna.
+		_, _, err := dcu1Client(l).Heading()
+		return err
 	default:
 		return pst.New(l.Host, l.Port).GoTo(0, false, -1)
 	}