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>

main/led_ring.h

@@ -1,11 +1,18 @@
 #include <stdint.h>
 
-typedef enum { LED_CMD_CLEAR, LED_CMD_SET_DIGIT, LED_CMD_SET_COLOR } led_mode_t;
+typedef enum {
+  LED_CMD_CLEAR,
+  LED_CMD_SET_DIGIT,
+  LED_CMD_SET_COLOR,
+  LED_CMD_PROGRESS
+} led_mode_t;
 
 typedef struct {
   led_mode_t mode;
   uint8_t value;
   uint8_t r, g, b;
+  uint8_t intensity;
+  uint8_t progress;
 } led_command_t;
 
 void led_ring_send_command(led_command_t *cmd);