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/engine/src/tests.rs

@@ -1148,6 +1148,9 @@ fn extrude_auto_operation() {
     assert!(rel(volume(&mut s), 40.0 * 30.0 * 15.0) < 1e-6);
     // Pulled out, it joins.
     assert_eq!(auto_operation(&s, &json!({"face": [20, 15, 15], "distance": 5})), Some("join"));
+    // Pushed in far past the bottom (halfway is below the box), it still cuts (#1257).
+    assert_eq!(auto_operation(&s, &json!({"face": [20, 15, 15], "distance": -50})), Some("cut"));
+    assert_eq!(auto_operation(&s, &json!({"face": [20, 15, 15], "distance": 50, "direction": "negative"})), Some("cut"));
     // A sketch on XY under the box: up goes into it (cut), down grows out of it (join), and a
     // profile beside the box still defaults to Join (New Body remains explicit).
     run(&mut s, "sketch.create", json!({"plane": "XY"}));