Implement the reviewed UI icon system and durable review workflow (#853)

Thanks @Nathan-Dane.

crates/engine/src/cmd/sketch_import.rs

@@ -15,13 +15,13 @@ use crate::{EngineError, Result, Session};
 pub static COMMANDS: &[CommandSpec] = &[
     CommandSpec::new("sketch.insert_dxf", "Insert DXF", insert_dxf)
         .at("SKETCH", "INSERT")
-        .icon("dxf")
+        .icon("sketch_dxf")
         .params(concat!("path | text: ASCII DXF (blocks expanded); at?: [x,y] offset, scale?, tolerance?: mm within which ends join (default 0.0001); plane?: (when no sketch is active, a new sketch on it; default XY)", created_doc!())),
     CommandSpec::new("sketch.insert_svg", "Insert SVG", insert_svg)
         .at("SKETCH", "INSERT")
         .icon("svg")
         .params(concat!("path | text: SVG; at?: [x,y] offset, scale?, tolerance?: mm within which ends join (default 0.0001); plane?: (when no sketch is active, a new sketch on it; default XY)", created_doc!())),
-    CommandSpec::new("sketch.export_dxf", "Save As DXF", export_dxf)
+    CommandSpec::new("sketch.export_dxf", "Save As DXF", export_dxf).icon("sketch_dxf")
         .noundo()
         .params("sketch?: id|name (default active); path?: file to write (else the DXF text is returned)"),
 ];