Trim and Break on ellipses, splines and conics: cut at the exact crossings (alternating projection onto both curves), pieces stay exact (Bézier spans as single-span control splines, conic arcs as conics); geom Seg2::split_at and closest_param

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

crates/engine/src/cmd/mod.rs

@@ -20,6 +20,7 @@ mod parameters;
 mod sketch;
 mod sketch_constraints;
 mod sketch_create;
+mod sketch_freeform;
 mod sketch_import;
 mod sketch_modify;
 mod sketch_project;