Replaces the hard-coded 2pt padding used when placing port name labels.
Configurable per element via port-name-padding on elmt (forwarded by
block and group), defaulting to 2pt to preserve existing layout.
Groups now accept ports/ports-margins like blocks. Port name labels
default to outside the group border (outside-port-names: true) so they
don't overlap child elements; set to false for block-style inside
labels.