fix(xref): show merged xref layers in Layer Manager on attach (#407)

XATTACH / XRELOAD merge the xref's layer and linetype tables into the
document, but the Layers panel cache only rebuilds via
sync_with_viewports - which nothing triggered until the file was saved
and reopened. Refresh the layer panel (and ribbon mirrors) right after
the merge in both paths.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/app/command_driver.rs

@@ -396,6 +396,10 @@ impl OpenCADStudio {
                         &mut self.tabs[i].scene,
                         &path,
                     );
+                    // Resolving the xref merged its layer / linetype tables
+                    // into the document — mirror them into the Layers panel
+                    // and ribbon dropdowns now, not on the next reopen (#407).
+                    self.refresh_layer_panel();
                 }
                 // Record where this draw ended so ARC_CONT can continue from it
                 // (before `entity` is moved into commit_entity).

src/app/commands/blocks.rs

@@ -540,6 +540,10 @@ impl OpenCADStudio {
                         self.tabs[i].scene.populate_hatches_from_document();
                         self.tabs[i].scene.populate_images_from_document();
                         self.tabs[i].scene.populate_meshes_from_document();
+                        // The reload may have merged new xref layers /
+                        // linetypes — mirror them into the Layers panel and
+                        // ribbon dropdowns (#407).
+                        self.refresh_layer_panel();
                     }
                 } else {
                     self.command_line