Add new STL file, update 3 button case, add battery meter functions

src/SmartCube/cubeBattery.h

@@ -0,0 +1,22 @@
+#define ADC_PIN A0  // ESP8266 ADC pin
+
+// Tuneable min and max battery voltages
+float VOLTAGE_MAX = 4.2;  // Full battery voltage
+float VOLTAGE_MIN = 3.0;  // Empty battery voltage
+
+const float R1 = 220000.0;  // 220k ohms
+const float R2 = 56000.0;   // 56k ohms
+const float ADC_MAX = 1023.0; // 10-bit ADC resolution
+const float V_REF = 1.0;      // ESP8266 ADC reference voltage
+
+float readBatteryVoltage() {
+  int rawADC = analogRead(ADC_PIN);
+  float voltage = (rawADC / ADC_MAX) * V_REF;
+  return voltage * (R1 + R2) / R2; // Scale to actual battery voltage
+}
+
+int batteryPercentage(float voltage) {
+  if (voltage >= VOLTAGE_MAX) return 100;
+  if (voltage <= VOLTAGE_MIN) return 0;
+  return (voltage - VOLTAGE_MIN) * 100 / (VOLTAGE_MAX - VOLTAGE_MIN); // Linear mapping
+}