feature: Gauge needle size should be adjustable

The needle in Gauge should be adjustable. When color thickness increases, the needle moves farther away from the tick labels, making the needle pointer hard to read.

Thin colors, needle is close:

Thick colors, needle is far:

Start by locating the Gauge implementation and its needle and color-thickness handling. Determine how needle size can be exposed as an adjustable option, then verify that thicker colors no longer make the pointer hard to read and that existing Gauge behavior remains intact.

Written by the indexing model from the issue text.