plot styles: the CTB/STB model and codec come from the codec crate

Cargo: codec d36331d, kernel 60f086b, graph 74aac56.

The table model and its file codec now live in `codec::plot_style`
(opencadcodec#53) and are re-exported here. What stays is where tables
come from: the plot styles folder, the session registry, the shipped
tables, and saving to disk, as the `PlotStyleTableExt` trait.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/mod.rs

@@ -66,6 +66,7 @@ pub use settings::MAX_SELECTED_GRIPS;
 /// as they are; only these two names are reachable externally.
 pub use settings::{CursorType, IsoPlane};
 
+use crate::io::plot_style::PlotStyleTableExt as _;
 use document::DocumentTab;
 
 use crate::modules::ModuleEvent;