Add UART LED_RING command for progress bar, digits, and clear.

Stop the main-loop digit demo so host-driven display persists; expose
clear/progress/digit modes with RGB and intensity via protobuf and goTool.

Co-authored-by: Cursor <cursoragent@cursor.com>

goTool/cmd_led_ring.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"powerpod/gotool/pb"
+)
+
+const (
+	ledRingModeClear    = 0
+	ledRingModeProgress = 1
+	ledRingModeDigit    = 2
+)
+
+func runLedRing(sp *serialPort, args []string) error {
+	fs := flag.NewFlagSet("led-ring", flag.ExitOnError)
+	mode := fs.String("mode", "progress", "clear, progress, or digit")
+	progress := fs.Uint("progress", 0, "fill level 0–100 (mode=progress)")
+	digit := fs.Uint("digit", 0, "digit 0–10 (mode=digit)")
+	r := fs.Uint("r", 0, "red 0–255")
+	g := fs.Uint("g", 255, "green 0–255")
+	b := fs.Uint("b", 0, "blue 0–255")
+	intensity := fs.Uint("intensity", 255, "brightness 0–255")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	var modeVal uint32
+	switch *mode {
+	case "clear":
+		modeVal = ledRingModeClear
+	case "progress":
+		modeVal = ledRingModeProgress
+	case "digit":
+		modeVal = ledRingModeDigit
+	default:
+		return fmt.Errorf("unknown -mode %q (clear, progress, digit)", *mode)
+	}
+
+	resp, err := sp.ledRingProgress(&pb.LedRingProgressRequest{
+		Mode:      modeVal,
+		Progress:  uint32(*progress),
+		Digit:     uint32(*digit),
+		R:         uint32(*r),
+		G:         uint32(*g),
+		B:         uint32(*b),
+		Intensity: uint32(*intensity),
+	})
+	if err != nil {
+		return err
+	}
+	fmt.Printf("success=%v mode=%d progress=%d digit=%d\n",
+		resp.GetSuccess(), resp.GetMode(), resp.GetProgress(), resp.GetDigit())
+	return nil
+}