fix(render): convert Trace::width through the UI scale, and fold the controller's tolerance conversion into Style::device()

include/plot/render/style.hpp

@@ -24,8 +24,13 @@ namespace plot::render {
 /// chosen LOD level depend on the display and not on the data. It is used raw.
 ///
 /// The same rule classifies the metrics that live outside this struct, which are
-/// logical too and converted by the same call: `Legend`'s pad, swatch, gap and
-/// margin, and the renderer's marker arm lengths and text offsets.
+/// logical too and converted by the same call:
+///
+///   * `Legend`'s pad, swatch, gap and margin;
+///   * `Trace`'s (and `TraceDesc`'s) `width` -- a stroke like `line_width_px`, and
+///     the one a plot draws most of, so leaving it raw would invert the
+///     trace/axis stroke hierarchy at any scale above 1;
+///   * the renderer's marker arm lengths and text offsets.
 struct Style {
   // --- colours: neither logical nor device, so nothing to scale ------------