Smart Extrude: direction from the picked side, and a Cut stays a Cut (#1257) (#1261)

* Smart Extrude: direction from the picked side, Cut into a body stays a Cut (#1257)

- A sketch profile (or a thin extrude's curve) extrudes toward the side it was
  picked from: from the bottom view it goes down. Body faces still go outward.
- The automatic operation is latched per side of the profile: a drag that starts
  into a body is a Cut and stays one past the far side; a Join does not become a
  Cut when it reaches another body. Passing through zero decides afresh for the
  new side.
- An explicit operation, Direction or Reverse ends the automatic choices.
- auto_operation also looks just past the profile, so a long cut through a body
  reads as a Cut from the start (the engine's operation: "auto" too).

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

* Scenario s07: the XZ profile seen from behind now extrudes toward the camera

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

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/lib.rs

@@ -136,6 +136,9 @@ pub(crate) mod sketch_text;
 mod sketch_text_handles;
 mod sketch_text_move;
 pub mod sketch_tools;
+pub mod smart_extrude;
+#[cfg(test)]
+mod smart_extrude_ui_tests;
 pub mod stand_up;
 pub mod theme;
 #[cfg(test)]