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/commands/draw.rs

@@ -1506,6 +1506,16 @@ impl OpenCADStudio {
                 self.tabs[i].active_cmd = Some(Box::new(new_cmd));
             }
 
+            "DIMCONSTRAINT" => {
+                use crate::modules::parametric::DimConstraintMenuCommand;
+                // Only the dynamic form exists here.
+                self.command_line
+                    .push_output("Current settings: Constraint form = Dynamic");
+                let new_cmd = DimConstraintMenuCommand;
+                self.command_line.push_info(&new_cmd.prompt());
+                self.tabs[i].active_cmd = Some(Box::new(new_cmd));
+            }
+
             "EDCONSTRAINT" => {
                 use crate::modules::parametric::EqualDistanceConstraintCommand;
                 let new_cmd = EqualDistanceConstraintCommand::new();