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/update/mod.rs

@@ -238,6 +238,8 @@ impl OpenCADStudio {
             Some(UnderlayLayers) => self.underlay_layers = None,
             Some(PdfImportSettings) => self.pdf_import_settings = None,
             Some(PdfImportFile) => self.pdf_import_file = None,
+            Some(ImportFile) => self.import_dialogs.file = None,
+            Some(DgnImport) => self.import_dialogs.dgn = None,
             Some(XrefAttach) => self.xref_attach = None,
             Some(WriteBlock) => self.wblock = None,
             Some(Hyperlink) => {
@@ -2406,6 +2408,7 @@ impl OpenCADStudio {
             }
 
             Message::PdfDialog(message) => self.update_pdf_dialog(message),
+            Message::ImportDialog(message) => self.update_import_dialog(message),
             Message::AttdefDialog(message) => self.on_attdef_dialog(message),
             Message::FieldDialog(message) => self.on_field_dialog(message),
             Message::RefEditDialog(message) => self.update_refedit_dialog(message),