Joints: gears, rack and pinion, and screws (#1524)

Motion links can carry a coupling (gear pair, rack and pinion, screw) whose ratio follows radii, picked round faces or pitch. Design format 23.

Co-authored-by: SychPL <SychPL@users.noreply.github.com>
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/ui-egui/src/lib.rs

@@ -25,6 +25,7 @@ pub mod design_properties;
 pub mod dialogs;
 pub mod dialogs_appearance;
 pub mod dialogs_assembly;
+pub mod dialogs_coupling;
 pub mod dialogs_library;
 pub mod dialogs_motion;
 pub mod dialogs_move;