- Fix display of invalid large values like 18446744073709544W
- macOS ioreg returns negative values as uint64 (two's complement)
- Detect overflow pattern (value > 2^63) and convert to signed
- Validate reasonable power range (-200W to 200W) for battery
- Add range validation for SystemPower (0 to 1000W)
Root cause: During charging, battery power is negative but ioreg
formats it as unsigned uint64, causing overflow. This fix properly
converts these values back to signed integers.