feat: Group sketch creation tools and remember variants per part (#589)

Sketch Create groups its drawing tools under Line, Rectangle, Circle, Arc, Slot, Polygon and Spline. Each family's main button starts the part's last-used variant and its caret lists the others; choices are per open part, kept across sketch sessions and tab switches, and never touch the design or undo history.

Co-authored-by: Karl Von Richter <karl@von-richter.net>

crates/ui-egui/src/workspace.rs

@@ -104,13 +104,14 @@ pub fn layout<'a>(tab: &str, panel: &str, specs: &[&'a CommandSpec]) -> Option<(
             &[
                 "sketch.line",
                 "sketch.rectangle.two_point",
-                "sketch.rectangle.three_point",
-                "sketch.rectangle.center",
                 "sketch.circle.center",
-                "sketch.circle.two_point",
+                "sketch.arc.three_point",
+                "sketch.slot.center_to_center",
+                "sketch.polygon.inscribed",
+                "sketch.spline.fit_point",
                 "sketch.point",
             ],
-            7,
+            8,
             tab,
         ),
         ("SOLID", "CONFIGURE") => (&["parameters.change", "config.table"], 2, tab),