ocs_doc_api: outstanding methods — loft + bulge-arc polyline profiles

- Loft{profiles} op (append-only); executor resolves each profile to curve sets
  all-or-nothing; backend loft() -> brep::loft on XY plane; facade solids().loft.
- entity_to_profile_curves: convert LwVertex.bulge to geom2d::Curve::Arc via
  bulge_arc_segment (theta = 4*atan(bulge)), so bulged polyline profiles sweep
  correctly instead of erroring Unsupported.
- spec loft; api_reference + binding_schema regenerated; mocks + baseline.
- Tests: loft_two_profiles_produces_solid, bulge_arc_polyline_profile_converts_to_arc
  (semicircle radius=5 for bulge=1) -> 612 host lib + 3 consistency green.

crates/ocs_doc_api/src/executor.rs

@@ -253,6 +253,22 @@ pub fn apply_op<B: DocApiBackend>(b: &mut B, op: Operation) -> ApiResult<Receipt
             b.finalize_op();
             OpOutcome::NewId(id)
         }
+        Operation::Loft { profiles } => {
+            // Resolve every profile to its curve set BEFORE push_undo (all-or-nothing).
+            if profiles.len() < 2 {
+                return Err(ApiError::validation(name, "loft needs >= 2 profiles"));
+            }
+            let mut sections = Vec::with_capacity(profiles.len());
+            for (i, p) in profiles.iter().enumerate() {
+                let curves = profile_curves(b, *p, name)
+                    .map_err(|e| at_index(name, i, e))?;
+                sections.push(curves);
+            }
+            b.push_undo(name);
+            let id = b.loft(&sections)?;
+            b.finalize_op();
+            OpOutcome::NewId(id)
+        }
     };
     Ok(Receipt {
         outcome: Some(outcome),