Line tool inference like Fusion: parallel or perpendicular to existing lines, on a line's extension and tangent to circles and arcs, shown with a dashed guide and the snap label; placing the point adds the constraint (the existing curve stays, the new line follows)

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

crates/ui-egui/src/viewport.rs

@@ -1272,6 +1272,7 @@ pub fn show(app: &mut SolveApp, ui: &mut egui::Ui) {
     overlays(app, &painter, &proj);
     crate::dim_view::show(app, ui, &painter, &proj);
     crate::sketch3d::show(app, &painter, &proj);
+    crate::inference::show(app, &painter, &proj);
     hover_highlight(app, &painter, &proj);
     points_2d(app, &painter, &proj);
     if let Some(bx) = app.viewport.boxsel {