Surface bodies: Patch, Stitch, Trim and Thicken

Kernel (surfaces):
- Bodies with an open shell are surface bodies (Body::is_surface).
- patch_region: a planar patch of a sketch region. patch_edges: a planar
  patch filling a closed loop of a body's edges.
- copy_faces: faces copied out as a surface.
- stitch: sew surfaces along coinciding edges, turning faces to agree; the
  result is a solid when it closes.
- trim: cut a surface by a plane or face and keep one side.
- thicken: offset planar and circular-cylindrical faces along their
  normals (one side or symmetric) into a solid. Plane copies slide;
  cylinder copies scale about the axis, exact for NURBS circles. Free
  edges get ruled walls. Faces meeting at a sharp edge are refused.

Doc features Patch, Stitch, Thicken (with operations) and SurfaceTrim;
engine commands FusionSurfacePatchCommand, FusionSurfaceStitchCommand,
FusionSurfaceThickenCommand and FusionSurfaceTrimCommand.

Tests (volumes):
- A 10x10 patch thickened by 2 gives 200, also symmetric.
- Half a cylinder side thickened outward gives half a ring; both halves
  inward give the full ring.
- Six faces of a box stitched back give 6000; an open box with its top
  patched from the edges, stitched, gives 6000.
- Trim keeps 30 or 70 of 100.
- Engine: patch, trim, thicken gives 140.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/doc/src/params.rs

@@ -223,6 +223,10 @@ impl FeatureKind {
                 }
             }
             FeatureKind::ReplaceFace { target, .. } => plane_inputs_mut(target, &mut v),
+            FeatureKind::Stitch { tolerance, .. } => v.push(("Tolerance", tolerance, L)),
+            FeatureKind::Thicken { thickness, .. } => v.push(("Thickness", thickness, L)),
+            FeatureKind::SurfaceTrim { plane, .. } => plane_inputs_mut(plane, &mut v),
+            FeatureKind::Patch { .. } => {}
             FeatureKind::Combine { .. }
             | FeatureKind::SheetBase { .. }
             | FeatureKind::SheetUnfold { .. }