Add software LiPo UV protection with energy-save boot.

Detect under-voltage on GPIO1/11, persist UV state in NVS, enter a minimal
power mode without ESP-NOW, and recover after charge; expose LED mode 6
battery-low for host testing via goTool.

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

main/pod_settings.h

@@ -2,6 +2,7 @@
 #define POD_SETTINGS_H
 
 #include "esp_err.h"
+#include <stdbool.h>
 #include <stdint.h>
 
 /** Initialize NVS (idempotent) and log stored settings. Call once early in app_main. */
@@ -16,4 +17,9 @@ uint32_t pod_settings_load_accel_deadzone(void);
 /** Apply NVS deadzone to BMA456 when the sensor is present. */
 void pod_settings_apply_accel_deadzone(void);
 
+/** LiPo under-voltage latch persisted across reboot (software UV protection). */
+bool pod_settings_is_uv_latched(void);
+esp_err_t pod_settings_set_uv_latched(bool latched);
+esp_err_t pod_settings_clear_uv_latched(void);
+
 #endif