One process list, or a closer look at each device

After using the first build, I wanted control over grouping and a better way to see individual drives and network connections. The app now remembers those choices, and the Performance sidebar lets me move between the whole picture and a single device.

Changelog

• Added Group by Type, off by default, with the choice remembered between launches.
• Added expandable Disk and Network sections whose headings show combined activity.
• Added individual physical-disk and network-adapter graphs and details, with APFS volumes identified under their shared physical disk.
• Return to the combined overview when collapsing a section containing the selected device; remember expanded sections across launches.
• Handle newly attached disks, removed devices, and counter resets without false activity spikes.