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 <[email protected]>

src/app/commands/fileops.rs

@@ -1,4 +1,6 @@
 use super::*;
+#[cfg(target_arch = "wasm32")]
+use crate::io::plot_style::PlotStyleTableExt as _;
 
 impl OpenCADStudio {
     pub(super) fn dispatch_fileops(&mut self, cmd: &str, i: usize) -> Option<Task<Message>> {