Surface Extrude: sheets from open curves and profile walls (#815)

surface.extrude sweeps open curve chains and profile boundaries along the sketch normal into a surface body (walls only, no caps). Saved under format 17.

Refs #757

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

crates/ui-egui/src/dialogs.rs

@@ -3610,7 +3610,7 @@ fn source_features(s: &Session, bodies: &[String]) -> Vec<String> {
 }
 
 /// The sketch holding all these curve ids (the active sketch first, never `not`).
-fn curves_sketch(app: &SolveApp, ids: &[String], not: Option<u64>) -> Option<u64> {
+pub(crate) fn curves_sketch(app: &SolveApp, ids: &[String], not: Option<u64>) -> Option<u64> {
     let st = app.session.world_state();
     let has =
         |sid: u64| st.sketch(sid).is_some_and(|ss| ids.iter().all(|id| ss.sketch.curve_index(id).is_some() || ss.sketch.wire_index(id).is_some()));