fix(ui): preserve construction tools and dashed feedback (#600)

Construction (X) keeps the active sketch tool, its picked points and inline values while switching line type, and drawing previews and hover show the same dashed pattern as committed construction and centre lines. Fixes #584 and #581.

Co-authored-by: lillith <[email protected]>

docs/book/src/guide/sketching.md

@@ -94,6 +94,11 @@ While drawing a fit spline, click its starting point after three distinct sample
 it smoothly. Right-click finishes an ordinary natural fit. Offset accepts both ellipse
 handles and dense fitted curves; the second click sets the side and distance from the curve.
 
+While drawing in a planar sketch, **Construction** (X) changes the line type without
+ending the tool or losing picked points and inline values. The preview and hover feedback
+keep construction dashes and centerline dash-dot patterns visible. With curves selected,
+Construction changes those curves as before.
+
 Enable **3D Sketch** in the Sketch Palette to draw lines, fit splines and points off the plane.
 While placing these points, you can snap to points on other visible sketches. For a bridge
 line, start Line and click an endpoint on each source sketch; each endpoint uses its source