feat(layout): MVSETUP sets a drawing up for plotting

In model space MVSETUP draws the sheet border at the drawing scale
(scale factor, paper width and height) and zooms to it, or switches to
a layout. On a layout it creates viewports in a bounding area (a single
one, a 2x2 engineering set of top/front/right/isometric views, or an
array with spacing), deletes picked objects, and scales picked
viewports to a paper/model unit ratio.

A viewport's fit to the model now measures the model along the
viewport's own view direction, so side and isometric views frame it
too.

Refs #1501

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

src/command.rs

@@ -1943,6 +1943,18 @@ pub enum CmdResult {
         p1: DVec3,
         p2: DVec3,
     },
+    /// Commit `entity`, then zoom to the given corner points; end command.
+    CommitAndZoom {
+        entity: EntityType,
+        p1: DVec3,
+        p2: DVec3,
+    },
+    /// Scale the given layout viewports to `factor` paper units per model
+    /// unit; end command.
+    ScaleViewports {
+        handles: Vec<Handle>,
+        factor: f64,
+    },
     /// Print a measurement result to the command line and end the command.
     Measurement(String),
     /// Print a measurement result and keep the command active.