DGNIMPORT: reference naming, cells, text placement, curves, references

Name clashes, DGNIMPORTMODE and prefixing as the reference names them;
V7 cell copies, unshared cells and mirrored placements as blocks;
justified text and text nodes placed at their justification points with
the reference's MTEXT contents; B-spline curves as splines and 3D arcs and
ellipses in their own planes; every V8 level as a layer; design models
only; reference attachments translated, ignored or attached as underlays.
The colour index palette comes from the codec fix it depends on.

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

src/app/update/file.rs

@@ -864,6 +864,7 @@ impl OpenCADStudio {
             ucs_view: crate::modules::view::view_cmd::ucs_view(),
             layout_create_viewport: crate::scene::layout_create_viewport(),
             pdf_shx_text: crate::modules::insert::pdf_shx_text::settings(),
+            dgn_import: crate::modules::insert::dgn_import::settings(),
             ncopy_bind: self.ncopy_bind,
             cursor_type: self.cursor_type,
             crosshair_color: self.crosshair_color,
@@ -1013,6 +1014,7 @@ impl OpenCADStudio {
         crate::modules::view::view_cmd::set_ucs_view(s.ucs_view);
         crate::scene::set_layout_create_viewport(s.layout_create_viewport);
         crate::modules::insert::pdf_shx_text::set_settings(s.pdf_shx_text.clone());
+        crate::modules::insert::dgn_import::set_settings(s.dgn_import);
         self.ncopy_bind = s.ncopy_bind;
         self.cursor_type = s.cursor_type;
         self.crosshair_color = s.crosshair_color;