Sketch drawing: a point snapped to a line's midpoint stays there ("mid:<line>" point arguments add a MidPoint constraint)

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

crates/ui-egui/src/viewport.rs

@@ -799,7 +799,7 @@ pub fn sketch_point_at(app: &SolveApp, proj: &Proj, pos: Pos2) -> Option<(Vec2,
     let (minor, _) = grid_step(app.cam.half_height());
     let step = minor / 10.0;
     if let Some(p) = crate::sketch_tools::refine_snap(app, proj, &ss.sketch, &ss.plane, lp) {
-        return Some((p, None));
+        return Some(p);
     }
     Some((Vec2::new((lp.x / step).round() * step, (lp.y / step).round() * step), None))
 }