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/battery_uv.h

@@ -11,10 +11,17 @@
 #define BATTERY_UV_ADC_MV 2300u
 /** ADC pin voltage (mV) at which charging is detected (4.0 V pack, rounded). */
 #define BATTERY_CHARGE_ADC_MV 3000u
+/**
+ * ADC readings below this are treated as no pack / external supply (not UV).
+ * Noise floor / open sense divider → near 0 mV.
+ */
+#define BATTERY_UV_ABSENT_ADC_MV 100u
 
 bool battery_uv_is_latched(void);
 bool battery_uv_reading_is_under(const board_lipo_reading_t *reading);
 bool battery_uv_reading_is_charged(const board_lipo_reading_t *reading);
+/** true when every valid channel is near 0 (externally powered / no LiPo). */
+bool battery_uv_reading_is_external(const board_lipo_reading_t *reading);
 
 /** true → enter UV energy-save path (does not return). */
 bool battery_uv_evaluate_boot(void);
@@ -38,6 +45,11 @@ static inline bool battery_uv_reading_is_charged(const board_lipo_reading_t *rea
   return false;
 }
 
+static inline bool battery_uv_reading_is_external(const board_lipo_reading_t *reading) {
+  (void)reading;
+  return false;
+}
+
 static inline bool battery_uv_evaluate_boot(void) { return false; }
 
 static inline void battery_uv_poll(const board_lipo_reading_t *reading) {