Add live battery power rate display

[git-anish]

Summary

This PR extends WhatWatt beyond negotiated adapter wattage and adds live battery charge/discharge power flow in a lightweight menu bar UI.

What changed

• show live battery charge or discharge rate in watts using AppleSmartBattery current and voltage
• keep low-power defaults by using event-driven refreshes with a 1s burst for 20s after charger-state changes and a 60s idle refresh otherwise
• add an Always Live Updates toggle
• add a lightweight Preferences... window for update tuning
• handle wrapped signed battery amperage values correctly on Intel Macs
• use a compact menu bar title format like 67W | ↑18.4W while charging and ↓18.4W when unplugged
• add a preference to show or hide 0W adapter state when unplugged

Notes

The battery telemetry appears to update on a slower cadence than the timer on some Macs, so 1 Hz refreshes do not always produce visibly new watt values every second. This PR keeps the UI lightweight while still making charger transitions observable.

This work was developed in a public fork here: https://github.com/git-anish/whatwatts

[SomeInterestingUserName]

Wow this is awesome! I will need some time to review your PR but I appreciate you finding this widget useful enough to make such an extensive contribution!