Add runtime UV protection toggle and treat near-zero sense as external power.

Per-pod NVS enable (default off) via UART/ESP-NOW/dashboard, and skip UV latch when LiPo ADC reads ~0 mV so USB/external supply still boots.

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

main/proto/esp_now_messages.proto

@@ -33,6 +33,8 @@ enum EspNowMessageType {
   ESPNOW_CLEAR_ID_BINDING = 23;
   /** Master → slave: accel/tap ESP-NOW send path (best_effort/fast/wait/reliable). */
   ESPNOW_SET_INPUT_SEND_MODE = 24;
+  /** Master → slave: enable/disable software LiPo UV protection (NVS). */
+  ESPNOW_SET_BATTERY_UV = 25;
 }
 
 message EspNowUnicastTest {
@@ -154,6 +156,12 @@ message EspNowInputSendMode {
   uint32 mode = 2;
 }
 
+/** Master → slave: software LiPo UV protection enable (persisted in NVS). */
+message EspNowBatteryUv {
+  uint32 client_id = 1; // 0 = all slaves; otherwise only matching slave_id applies
+  bool enabled = 2;
+}
+
 /** Slave → master: LiPo voltages (periodic ~30 s and on query). */
 message EspNowBatteryReport {
   uint32 client_id = 1;
@@ -225,5 +233,6 @@ message EspNowMessage {
     EspNowAssignId assign_id = 23;
     EspNowClearIdBinding clear_id_binding = 24;
     EspNowInputSendMode input_send_mode = 25;
+    EspNowBatteryUv battery_uv = 26;
   }
 }