Power Monitor: clearer behaviour on ports without live metering

What's fixed

Power Monitor no longer estimates a voltage it cannot measure. On Macs where macOS does not expose live per-port power metering (notably the MagSafe port), the Power Monitor previously fell back to deriving a voltage from the port controller's contracted data and plotting it on the live graph. That derived figure could be inaccurate. It now shows the port's maximum with a clear "Live per-port metering is not available on this hardware" note instead of charting a value it cannot actually measure, and the whatcable monitor CLI shows -- for these ports instead of a derived figure. Thanks to @NaiveTomcat for the report (#146).
Pro badge contrast. The Pro badge now meets WCAG AA contrast; it was orange on grey and hard to read. (#142)

More cables in the database. Around 20 newly reported cables added to the bundled known-cables database, so more cables resolve to a known brand and model.
Website refresh. The whatcable.uk pages got a content and mobile-responsiveness pass.

brew upgrade --cask whatcable, or download WhatCable.zip from this release page and drag the new .app into /Applications.