Copy, cut and paste sketch geometry (Ctrl+C/X/V, context menu) (#1500)

* Copy, cut and paste sketch geometry (Ctrl+C/X/V, context menu)

Sketch geometry had no copy or paste: Ctrl+C / Ctrl+X / Ctrl+V arrive as
clipboard events that nothing handled, and the sketch context menu had no
Copy, Cut or Paste.

- sketch.copy / sketch.cut / sketch.paste: lines, arcs, circles, ellipses,
  splines, conics, points and text. Constraints and dimensions wholly among
  the copied entities come along (each dimension gets its own parameter
  with the same expression); ones that reach outside, fixes and pattern or
  offset relations are dropped. Paste goes centred at `at`, by
  `translate`, or offset from the original (same sketch) / at the same
  coordinates (another sketch, on its plane). One undo step; the pasted
  geometry is selected.
- Ctrl+C / Ctrl+X / Ctrl+V in a sketch (paste at the cursor), and Cut,
  Copy and Paste in the sketch context menu. Outside a sketch Ctrl+C /
  Ctrl+V copy and paste the selected timeline features. A copy also puts a
  line of text on the system clipboard so the next Ctrl+V is delivered.

Fixes #1480

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

* Keep a pasted text's height and angle expressions, drop its place's

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/mod.rs

@@ -64,6 +64,7 @@ pub(crate) use sketch::author_path_for_rebind;
 pub(crate) use sketch::created as sketch_created;
 mod sketch_3d;
 mod sketch_canvas;
+pub mod sketch_clipboard;
 mod sketch_constraints;
 mod sketch_create;
 mod sketch_freeform;
@@ -252,6 +253,7 @@ pub fn command_specs() -> Vec<&'static CommandSpec> {
     v.extend(delete::COMMANDS.iter());
     v.extend(edit::COMMANDS.iter());
     v.extend(clipboard::COMMANDS.iter());
+    v.extend(sketch_clipboard::COMMANDS.iter());
     v.extend(script::COMMANDS.iter());
     v.extend(parameters::COMMANDS.iter());
     v.extend(file::COMMANDS.iter());