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.

internal/rotator/dcu1/dcu1.go

@@ -0,0 +1,158 @@
+// Package dcu1 drives rotator controllers that speak the Hy-Gain DCU-1 protocol,
+// over a serial COM port (or a raw TCP socket, e.g. a serial-over-IP bridge).
+//
+// DCU-1 is used by the Hy-Gain DCU-1, the Idiom Press Rotor-EZ, Green Heron
+// controllers, and the RotorCard DXA (hamsupply) for Yaesu DXA rotors. It is a
+// DIFFERENT command set from Yaesu GS-232 (see internal/rotator/gs232):
+// semicolon-terminated, azimuth only.
+//
+// Commands (';' terminated — roundTrip appends the ';'):
+//
+//	AP1nnn   set the target bearing nnn (000-359)
+//	AM1      rotate to the target (some controllers move on AP1 alone; AM1 is
+//	         harmless and makes the Rotor-EZ/DCU-1 variants that need it work)
+//	AI1      query the current bearing → the reply carries the 3-digit azimuth
+//
+// The base DCU-1 set has no dedicated stop; Stop re-commands the current bearing,
+// which halts rotation.
+package dcu1
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"go.bug.st/serial"
+)
+
+const (
+	dialTimeout = 3 * time.Second
+	ioTimeout   = 2 * time.Second
+)
+
+// Client is a stateless per-call sender, mirroring the gs232/pst/rotgenius idiom.
+// Exactly one of (Host, Port) or ComPort is used.
+type Client struct {
+	Host    string
+	Port    int
+	ComPort string // serial transport: "COM5" etc.
+	// Baud varies by controller (a Hy-Gain DCU-1 is 4800; Green Heron / RotorCard
+	// can differ). Zero keeps 4800.
+	Baud int
+}
+
+// New returns a TCP Client (a serial-over-IP bridge in front of the controller).
+func New(host string, port int) *Client {
+	if host == "" {
+		host = "127.0.0.1"
+	}
+	if port <= 0 || port > 65535 {
+		port = 4001
+	}
+	return &Client{Host: host, Port: port}
+}
+
+// NewSerial returns a Client over the controller's COM port.
+func NewSerial(comPort string, baud int) *Client {
+	return &Client{ComPort: comPort, Baud: baud}
+}
+
+// roundTrip opens a connection, sends one ';'-terminated command and (when
+// wantReply) reads until a 3-digit bearing is present. cmd must NOT carry the
+// ';'.
+func (c *Client) roundTrip(cmd string, wantReply bool) (string, error) {
+	var conn io.ReadWriteCloser
+	if c.ComPort != "" {
+		baud := c.Baud
+		if baud <= 0 {
+			baud = 4800
+		}
+		sp, err := serial.Open(c.ComPort, &serial.Mode{BaudRate: baud})
+		if err != nil {
+			return "", fmt.Errorf("open rotator %s @ %d baud: %w", c.ComPort, baud, err)
+		}
+		_ = sp.SetReadTimeout(200 * time.Millisecond)
+		conn = sp
+	} else {
+		nc, err := net.DialTimeout("tcp", net.JoinHostPort(c.Host, strconv.Itoa(c.Port)), dialTimeout)
+		if err != nil {
+			return "", fmt.Errorf("connect DCU-1 %s:%d: %w", c.Host, c.Port, err)
+		}
+		_ = nc.SetDeadline(time.Now().Add(ioTimeout))
+		conn = nc
+	}
+	defer conn.Close()
+	if _, err := conn.Write([]byte(cmd + ";")); err != nil {
+		return "", fmt.Errorf("send %q: %w", cmd, err)
+	}
+	if !wantReply {
+		return "", nil
+	}
+	buf := make([]byte, 64)
+	var sb strings.Builder
+	deadline := time.Now().Add(ioTimeout)
+	for time.Now().Before(deadline) {
+		n, err := conn.Read(buf)
+		if n > 0 {
+			sb.Write(buf[:n])
+			// The DCU-1 reply carries the bearing as three digits (framing varies —
+			// ";nnn", "nnn;", "+0nnn"). Stop once we have them rather than on a
+			// specific terminator, so any flavour reads cleanly.
+			if azRe.MatchString(sb.String()) {
+				break
+			}
+		}
+		// A serial read that times out returns (0, nil) — keep polling until the
+		// overall deadline; a real error ends the read.
+		if err != nil {
+			break
+		}
+	}
+	line := strings.TrimSpace(sb.String())
+	if line == "" {
+		return "", fmt.Errorf("no reply to %q", cmd)
+	}
+	return line, nil
+}
+
+// GoTo points the antenna at az (0-359): set the target, then rotate.
+func (c *Client) GoTo(az int) error {
+	az = ((az % 360) + 360) % 360
+	if _, err := c.roundTrip(fmt.Sprintf("AP1%03d", az), false); err != nil {
+		return err
+	}
+	_, err := c.roundTrip("AM1", false)
+	return err
+}
+
+// Stop halts rotation. The base DCU-1 set has no stop command, so re-command the
+// current bearing — the controller stops when the target equals where it is.
+func (c *Client) Stop() error {
+	az, _, err := c.Heading()
+	if err != nil {
+		return err
+	}
+	_, err = c.roundTrip(fmt.Sprintf("AP1%03d", az), false)
+	return err
+}
+
+// azRe matches the 3-digit bearing in any of the DCU-1 reply framings.
+var azRe = regexp.MustCompile(`(\d{3})`)
+
+// Heading queries the current azimuth. Returns the raw reply for diagnostics.
+func (c *Client) Heading() (az int, raw string, err error) {
+	raw, err = c.roundTrip("AI1", true)
+	if err != nil {
+		return 0, raw, err
+	}
+	m := azRe.FindStringSubmatch(raw)
+	if m == nil {
+		return 0, raw, fmt.Errorf("unrecognised azimuth reply %q", raw)
+	}
+	az, _ = strconv.Atoi(m[1])
+	return az % 360, raw, nil
+}