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/update/file.rs

@@ -1,6 +1,7 @@
 //! `file` arms and helpers, split out of the original `update.rs` (#mechanical decomposition).
 
 #![allow(unused_imports)]
+use crate::io::plot_style::PlotStyleTableExt as _;
 use super::util::*;
 use super::{format_size, VIEWCUBE_HIT_SIZE};
 use crate::app::helpers::{

src/app/update/mod.rs

@@ -1,3 +1,4 @@
+use crate::io::plot_style::PlotStyleTableExt as _;
 use super::{ArrowKey, Message, OpenCADStudio, TextEntryMode};
 use crate::command::CadCommand;
 use crate::scene::VIEWCUBE_DRAW_PX;