IMPORT: 3D Studio files

A .3ds file opens the 3D Studio Import window: the file's objects with
their kind and material count, filtered by kind or name, checked one by
one or all at once, where to put them on layers and what a mesh with
several materials becomes. Checked meshes come in as polyface meshes on
the chosen layers with materials made from the file's colours, cameras
as named views; a mesh with several materials is split, given its first
material, given none, or asked about on the command line. Automation
drives the window with tds_import_dialog.

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

src/app/command_driver/mod.rs

@@ -654,6 +654,11 @@ impl OpenCADStudio {
                 self.tabs[i].snap_result = None;
                 return self.run_dgn_import(i, request);
             }
+            CmdResult::TdsImport(request) => {
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.run_tds_import(i, request);
+            }
             CmdResult::PdfImportFile(import) => {
                 self.tabs[i].scene.clear_preview_wire();
                 self.tabs[i].active_cmd = None;