fix(ui): preview actual polygon outlines while drawing (#583)

Inscribed, circumscribed and edge polygon tools preview their actual outline (side count and orientation) while drawing, with the current line type, instead of only the support circle. Preview work is bounded. Fixes #520.

Co-authored-by: lillith <35337584+0xlillith@users.noreply.github.com>

docs/book/src/guide/sketching.md

@@ -31,6 +31,10 @@ fit-point and control-point splines, conics, points and text. **Construction** (
 into reference geometry that doesn't form profiles. Modify tools include trim (T), extend, break,
 fillet, chamfer, offset (O), mirror, patterns, move/copy and scale.
 
+Polygon tools show their edge outline while positioning the second point, so the orientation
+can be checked before placement. Inscribed and circumscribed polygons retain their support
+circle and update the outline when the inline **Sides** value changes.
+
 **Text** is set in the built-in font (Liberation Sans) unless it is given another: `sketch.text` and
 `sketch.edit_text` take a `font`, the family or full name of an installed font ("DejaVu Sans") or the path
 of a `.ttf` / `.otf` file, and the **Edit Text** dialog has a **Font** field for it. An unknown font is an