HeaderPill used the bordered/transparent .hive-pill shape while every
other chip in .agent-header-pills (StatusChips, MetaNav's trigger) is
@hive/shared's filled Badge (.ui-badge) -- the one visibly hollow pill
in a row of filled ones. Restyled .header-pill with .ui-badge's own
values (filled --purple-dim background, no border, matching radius/
padding/hover) instead of a new shape, and dropped hive-pill from the
markup since it no longer describes what this component looks like.