feat(ribbon): contextual Block Editor tab while editing a block

Opening the block editor brings up a Block Editor ribbon tab with
Edit / Save / Discard, Attribute Definition, and the geometric,
dimensional and parameter tools that drive parametric blocks. The tab
is only listed while a block editor session is open, and leaving the
session returns to the tab that was active before.

Refs #509

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/modules/registry.rs

@@ -23,6 +23,7 @@ pub fn all_modules() -> Vec<Box<dyn CadModule>> {
         Box::new(super::view::ViewModule),
         Box::new(super::manage::ManageModule),
         Box::new(super::layout::LayoutModule),
+        Box::new(super::block_editor::BlockEditorModule),
     ]
 }