SWEEP: sweep from the picked path end; kernel run faces and placed ends

- An open path is swept from its end nearest the pick point (in plan), as
  the reference does; the record keeps the original path and the placed
  frame marks the start.
- Kernel from ramox81/cadkernel 1df75f5: one face per path run for
  twisted, scaled and spline sweeps, placed records swept from the placed
  end, end caps without pcurves.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/command.rs

@@ -1356,6 +1356,9 @@ pub struct SweepOptions {
     pub scale: f64,
     /// Total twist along the path, in radians.
     pub twist_angle: f64,
+    /// Where the path was picked: an open path is swept from its end nearest
+    /// this point (seen from above), as the reference does.
+    pub path_pick: Option<DVec3>,
 }
 
 impl Default for SweepOptions {
@@ -1366,6 +1369,7 @@ impl Default for SweepOptions {
             base_point: None,
             scale: 1.0,
             twist_angle: 0.0,
+            path_pick: None,
         }
     }
 }