Dimensional constraints: dynamic dimension persistence, lock mark, display variables, DIMCONSTRAINT

The dynamic dimension of a dimensional constraint is now linked in the
drawing file (AcDbAssocDependency + AcDbAssocDimDependencyBody on the
constraint node), reread on load, hidden by DCHIDE/DYNCONSTRAINTDISPLAY
and never plotted; it carries a lock mark before its text. New
CONSTRAINTNAMEFORMAT and DYNCONSTRAINTDISPLAY variables and the
DIMCONSTRAINT option front end. A transformed entity whose own end points
a driving dimension measures keeps only the first constraint point, so a
scaled line returns to its dimension value.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/app/command_driver.rs

@@ -3686,6 +3686,8 @@ impl OpenCADStudio {
                     &[first],
                     self.constraint_solve_mode,
                 );
+                // DYNCONSTRAINTDISPLAY 0 also keeps a new dynamic dimension off screen.
+                self.tabs[i].scene.refresh_hidden_dynamic_dimensions();
                 self.tabs[i].dirty = true;
                 self.tabs[i].active_cmd = None;
                 self.tabs[i].snap_result = None;