- The halo no longer grows during the fade: radius is constant at
size + 9px; only its opacity fades in/out over ~180ms.
- The hover name is drawn opaque in the bright color instead of
cross-fading over the muted resting label. Partial-alpha text
oscillated whenever hover toggles rapidly at a small node's hit
boundary (sigma fires enterNode/leaveNode on every state change) —
an un-animated color can't flicker.