feat(render): logical style metrics with a UI scale, so chrome has a consistent physical size

include/plot/render/embedded_mono_font.hpp

@@ -52,8 +52,9 @@ class EmbeddedMonoFont final : public TextBackend {
   /// Top of the cell to the baseline, in font pixels.
   f32 ascent() const override;
   /// `kEmPx`: the size the face was baked at. The renderer scales a run by
-  /// `Style::axis_font_px / em_px()`, so the same backend draws the size the
-  /// style asked for whatever it was baked at.
+  /// `Style::device(Style::axis_font_px) / em_px()` -- the style's logical em in
+  /// device pixels over this em -- so the same backend draws the size the style
+  /// asked for, on any DPI, whatever it was baked at.
   f32 em_px() const override;
 
   /// The glyph for `codepoint`: its atlas cell as a normalised rect, no extra