zeroOffset

[Mirza-Samad-Ahmed-Baig]

The core issue was zeroOffset = 0.0 resets the calibration every time you lift your finger. This makes the scale completely unusable because:

1. When you calibrate the scale by pressing "Zero Scale", it sets the zeroOffset
2. But as soon as you lift your finger to place an object, the calibration is lost
3. This defeats the entire purpose of a scale

Additionally, I added:

1. Persistence: The calibration is now saved to UserDefaults, so it persists between app launches
2. Reset function: Added a proper resetCalibration() method for when users actually want to reset
3. Reset button: Added a UI button to reset calibration when needed