Nodes that aren't reachable from the anchor at all (no path of links to
it) used to render with no overlay — they sat at full brightness while
everything else was darkened. Now they get the last band's treatment:
violet outline, same body-darken curve as the further-band nodes when
the focus slider is up. Last band's legend label updated to
"6+ hops / unconnected" so the colour key matches the behaviour.
Guard added so when no anchor is set we still don't paint anything —
the "treat unreachable as 6+" rule only applies once the user has
anchored on a node.
shootthesound
b39070be72