feat(relay): accept a full URL host so relays work behind an HTTPS proxy

Network relay boards (WebSwitch/KMTronic/Dingtian) were always reached at
http://<host>, so a board on the LAN behind a reverse proxy — the common remote
setup where the operator's 80/443 already go to Nginx Proxy Manager — couldn't be
reached from outside. relayBase() now keeps a scheme the operator supplies
(https://relay.example.com, optional sub-path) and only defaults to http:// for a
bare host/host:port. UI hint + test added.

internal/relaydev/relaydev.go

@@ -61,6 +61,22 @@ func get(ctx context.Context, url, user, pass string) ([]byte, error) {
 	return body, nil
 }
 
+// relayBase turns a configured host into the base URL of a network relay board.
+// A bare host or host:port keeps the default http:// (the boards serve plain
+// HTTP on their LAN). A host that already carries a scheme is used verbatim, so
+// a board can be reached through an HTTPS reverse proxy — e.g. a Nginx Proxy
+// Manager entry "https://relay.example.com" fronting the LAN board's port 80,
+// which is how an operator reaches shack relays from outside when 80/443 are
+// already taken by the proxy. A trailing slash is trimmed so path parts append
+// cleanly; an optional sub-path in the host is preserved (a sub-path proxy).
+func relayBase(host string) string {
+	h := strings.TrimSpace(host)
+	if strings.HasPrefix(h, "http://") || strings.HasPrefix(h, "https://") {
+		return strings.TrimRight(h, "/")
+	}
+	return "http://" + h
+}
+
 // ── WebSwitch 1216H ────────────────────────────────────────────────────
 
 type webswitch struct {
@@ -82,7 +98,7 @@ func (w *webswitch) Set(ctx context.Context, relay int, on bool) error {
 	if on {
 		action = "on"
 	}
-	_, err := get(ctx, fmt.Sprintf("http://%s/relaycontrol/%s/%d", w.host, action, relay), "", "")
+	_, err := get(ctx, fmt.Sprintf("%s/relaycontrol/%s/%d", relayBase(w.host), action, relay), "", "")
 	return err
 }
 
@@ -93,7 +109,7 @@ func (w *webswitch) Status(ctx context.Context) ([]bool, error) {
 		sel.WriteString(strconv.Itoa(i))
 		sel.WriteByte('$')
 	}
-	body, err := get(ctx, fmt.Sprintf("http://%s/relaystate/get2/%s", w.host, sel.String()), "", "")
+	body, err := get(ctx, fmt.Sprintf("%s/relaystate/get2/%s", relayBase(w.host), sel.String()), "", "")
 	if err != nil {
 		return nil, err
 	}
@@ -140,7 +156,7 @@ func (k *kmtronic) Set(ctx context.Context, relay int, on bool) error {
 		state = "01"
 	}
 	// FF<rr><ss>: e.g. FF0101 = relay 1 on, FF0800 = relay 8 off.
-	_, err := get(ctx, fmt.Sprintf("http://%s/FF%02d%s", k.host, relay, state), k.user, k.pass)
+	_, err := get(ctx, fmt.Sprintf("%s/FF%02d%s", relayBase(k.host), relay, state), k.user, k.pass)
 	return err
 }
 
@@ -154,7 +170,7 @@ type kmStatus struct {
 }
 
 func (k *kmtronic) Status(ctx context.Context) ([]bool, error) {
-	body, err := get(ctx, fmt.Sprintf("http://%s/status.xml", k.host), k.user, k.pass)
+	body, err := get(ctx, fmt.Sprintf("%s/status.xml", relayBase(k.host)), k.user, k.pass)
 	if err != nil {
 		return nil, err
 	}
@@ -259,8 +275,8 @@ func (d *dingtian) Set(ctx context.Context, relay int, on bool) error {
 	}
 	// type=0 is plain ON/OFF (1 = jogging, 2 = delay, 3 = flash, 4 = toggle),
 	// and time is then unused.
-	body, err := d.getCGI(ctx, fmt.Sprintf("http://%s/relay_cgi.cgi?type=0&relay=%d&on=%d&time=0&pwd=%s&",
-		d.host, relay-1, state, d.pwd))
+	body, err := d.getCGI(ctx, fmt.Sprintf("%s/relay_cgi.cgi?type=0&relay=%d&on=%d&time=0&pwd=%s&",
+		relayBase(d.host), relay-1, state, d.pwd))
 	if err != nil {
 		return err
 	}
@@ -274,7 +290,7 @@ func (d *dingtian) Set(ctx context.Context, relay int, on bool) error {
 }
 
 func (d *dingtian) Status(ctx context.Context) ([]bool, error) {
-	body, err := d.getCGI(ctx, fmt.Sprintf("http://%s/relay_cgi_load.cgi", d.host))
+	body, err := d.getCGI(ctx, fmt.Sprintf("%s/relay_cgi_load.cgi", relayBase(d.host)))
 	if err != nil {
 		return nil, err
 	}

internal/relaydev/relaydev_test.go

@@ -172,3 +172,19 @@ func TestDingtianSetRefusalIsAnError(t *testing.T) {
 		t.Fatal("a refused command answered HTTP 200 and was reported as success")
 	}
 }
+
+func TestRelayBase(t *testing.T) {
+	cases := map[string]string{
+		"192.168.1.5":                  "http://192.168.1.5",
+		"192.168.1.5:8080":             "http://192.168.1.5:8080",
+		"https://relay.example.com":    "https://relay.example.com",
+		"https://relay.example.com/":   "https://relay.example.com",
+		"http://relay.example.com/sw/": "http://relay.example.com/sw",
+		"  relay.local  ":              "http://relay.local",
+	}
+	for in, want := range cases {
+		if got := relayBase(in); got != want {
+			t.Errorf("relayBase(%q) = %q, want %q", in, got, want)
+		}
+	}
+}