Add LED ring control per client and broadcast over REST and WebSocket.

Solid color mode fills all ring LEDs; master routes UART commands to slaves
via ESPNOW_LED_RING. goTool exposes POST /api/led-ring, WebSocket set_led_ring,
and a dashboard LED panel with master/slave/all targets.

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

main/led_ring.c

@@ -116,6 +116,8 @@ void vTaskLedRing(void *pvParameters) {
         for (int i = 0; i < digit.count; i++) {
           led_strip_set_pixel(led_ring, RING_LEDS - digit.leds[i], r, g, b);
         }
+      } else if (cmd.mode == LED_CMD_SET_COLOR) {
+        ring_fill_color(r, g, b);
       } else if (cmd.mode == LED_CMD_PROGRESS) {
         uint32_t lit = ((uint32_t)cmd.progress * RING_LEDS + 50) / 100;
         if (lit > RING_LEDS) {