Reference case for a fillet with a B-spline radius (#810)

Adds oracle case 81 (a box edge rounded at a clamped cubic B-spline radius) with analytic expected values, and passes spline fillets through recipes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/solidcraft-cli/src/recipe.rs

@@ -517,13 +517,15 @@ pub fn to_script(recipe: &Value) -> Result<Value, String> {
                 let mut p = json!({"edges": edge_points(f), "radius": f.get("radius"), "name": name});
                 // Constant radius (the default), chord length, or a radius varying along each edge
                 // (`radius` at the end nearest `start`, `radius2` at the other, `mid` between,
-                // `smooth`); `fit` for a radius too large for the geometry.
+                // `smooth`), or a B-spline along each edge (`radius` its first control radius,
+                // `radii` the rest, `knots`); `fit` for a radius too large for the geometry.
                 match f.get("type").and_then(Value::as_str) {
                     Some("chord_length") => p["type"] = json!("chord"),
                     Some("variable_radius") => p["type"] = json!("variable"),
+                    Some("spline_radius") => p["type"] = json!("spline"),
                     _ => {}
                 }
-                for key in ["radius2", "start", "mid", "smooth", "fit"] {
+                for key in ["radius2", "start", "mid", "smooth", "fit", "radii", "knots"] {
                     if let Some(v) = f.get(key) {
                         p[key] = v.clone();
                     }