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 <noreply@anthropic.com>

src/app/commands/mod.rs

@@ -10,6 +10,7 @@ mod blocks;
 mod blockvars;
 mod bvisibility;
 mod count;
+mod dgn_import;
 mod dim;
 pub(crate) mod display;
 mod draw;
@@ -336,6 +337,9 @@ impl OpenCADStudio {
         if let Some(t) = self.dispatch_xref_attach(cmd, i) {
             return Some(t);
         }
+        if let Some(t) = self.dispatch_import(cmd, i) {
+            return Some(t);
+        }
         if let Some(t) = self.dispatch_bvisibility(cmd, i) {
             return Some(t);
         }
@@ -921,6 +925,9 @@ inventory::submit!(crate::command::CommandRegistration {
         "NEW",
         "QNEW",
         "OBJIMPORT",
+        "IMPORT",
+        "DGNIMPORT",
+        "-DGNIMPORT",
         "OPEN",
         "ORTHO",
         "P",