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/client_registry.h

@@ -47,6 +47,8 @@ typedef struct {
   uint32_t lipo1_mv;
   uint32_t lipo2_mv;
   uint32_t battery_updated_at;
+  /** Master cache: software UV protection enabled on slave (default false). */
+  bool uv_protection_enabled;
   /** Master: last ESPNOW_ASSIGN_ID send time (rate-limit resends). */
   uint32_t last_assign_sent_at;
 } client_info_t;
@@ -119,6 +121,11 @@ esp_err_t client_registry_get_tap_config(uint32_t client_id,
                                          bma456_tap_config_t *cfg_out);
 size_t client_registry_set_tap_config_all(const bma456_tap_config_t *cfg);
 
+esp_err_t client_registry_set_uv_protection(uint32_t client_id, bool enabled);
+esp_err_t client_registry_get_uv_protection(uint32_t client_id,
+                                            bool *enabled_out);
+size_t client_registry_set_uv_protection_all(bool enabled);
+
 /** Store latest accel sample from a slave (matched by sender MAC). */
 esp_err_t client_registry_update_accel(const uint8_t mac[CLIENT_MAC_LEN],
                                        uint32_t slave_id, int16_t x, int16_t y,