Add round vs straight box edges property

The property is already [available in the chart definition](https://github.com/jodigiordano/gg/blob/main/core/schemas/subsystem.json#L68) and [the UI is nearly done](https://github.com/jodigiordano/gg/blob/main/app/src/properties/borderEdges.ts) but the look & feel of round edges need work.