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/canvas.rs

@@ -159,7 +159,7 @@ fn poly_mid(poly: &[Vec2]) -> Option<(Vec2, Vec2)> {
     last
 }
 
-fn profile_plane(app: &SolveApp, sketch: u64) -> Option<solidcraft_engine::geom::Plane> {
+pub(crate) fn profile_plane(app: &SolveApp, sketch: u64) -> Option<solidcraft_engine::geom::Plane> {
     let component = app.session.doc.feature(sketch)?.component;
     let state = app.session.model.state();
     let plane = state.sketch(sketch)?.plane;