import: IMPORT window and DGNIMPORT converting DGN models to drawing objects

The DGN V7/V8 readers expose each element (level, symbology, geometry,
complex chains, text nodes, shared cells). DGNIMPORT / -DGNIMPORT convert a
model with the Standard mapping into a new drawing; IMPORT opens the
Import File window and routes PDF and DGN files to their importers.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/command_driver/mod.rs

@@ -627,6 +627,12 @@ impl OpenCADStudio {
                 self.apply_xclip(i, inserts, action);
             }
             CmdResult::OpenPdfImportSettings => self.open_pdf_import_settings(),
+            CmdResult::DgnImport(request) => {
+                self.tabs[i].scene.clear_preview_wire();
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                return self.run_dgn_import(i, request);
+            }
             CmdResult::PdfImportFile(import) => {
                 self.tabs[i].scene.clear_preview_wire();
                 self.tabs[i].active_cmd = None;