feat(ucs): build axis-aligned shapes in the active UCS

Commands that construct geometry with implicit axis directions ignored
the UCS, so a rectangle drawn under a rotated UCS came out world-aligned.
Give commands the UCS and build square to it:

- CadCommand::set_ucs(Mat4) (UCS→wire affine, default no-op); the host
  pushes the current UCS via App::push_ucs_to_cmd before each point /
  preview / text dispatch (DocumentTab::ucs_wire_affine, identity outside
  model space). New axis-aligned commands just override set_ucs.
- RECT (two-corner) and RECT_CEN (center) place their derived corners on
  the UCS axes (ucs_box_corners / ucs_box_around_center).
- ARRAYRECT row/column offsets run along the UCS axes.

RECT_ROT, POLYGON, and ELLIPSE already take their orientation from picked
points, so they need no change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/command/mod.rs

@@ -416,6 +416,13 @@ pub trait CadCommand: Send {
     /// Current prompt string to display in the command line.
     fn prompt(&self) -> String;
 
+    /// Push the active UCS into the command as a UCS→render(wire)-space affine
+    /// (identity = plain WCS). Commands that build axis-aligned geometry (RECT,
+    /// rectangular ARRAY, …) override this to store it and rotate their implicit
+    /// axes into the UCS; most commands work purely from picked points and
+    /// ignore it. Called before each point / preview dispatch.
+    fn set_ucs(&mut self, _ucs: glam::Mat4) {}
+
     /// Called when the user left-clicks in the viewport (point pick).
     fn on_point(&mut self, pt: Vec3) -> CmdResult;