Wire up the Properties panel's Parameters section

PropValue::ParamRow/ParamAddRow, the PropParamInput/Commit/Delete/AddNew
messages, their command_driver handlers (on_prop_param_commit/_delete/
_add_new, resolve_named_parameter_edit), and their render functions all
already existed — but nothing ever constructed the "Parameters" section
that would route data to them, so the whole inline add/rename/redefine/
delete workflow was unreachable from the UI. Adds that missing section
to the no-selection page in refresh_properties, alongside a new
PropValue::ParamsVisibilityToggle header row (mirrors the existing
show_constraint_values setting) for toggling whether constraint pills
show their driven value/parameter name.

Users can now manage named parameters inline in the Properties panel
(live resolved values, add/rename/redefine/delete) as an alternative to
the separate PARAMETERS modal, which continues to work unchanged.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/scene/selection.rs

@@ -750,7 +750,8 @@ impl Scene {
                                 | PropValue::FieldLwVaries { .. }
                                 | PropValue::EntityLink { .. }
                                 | PropValue::ParamRow { .. }
-                                | PropValue::ParamAddRow => continue,
+                                | PropValue::ParamAddRow
+                                | PropValue::ParamsVisibilityToggle(_) => continue,
                             }
                         };
                         out.push(choice(prop.field, prop.label, editor));
@@ -887,7 +888,8 @@ impl Scene {
                     | PropValue::FieldLwVaries { .. }
                     | PropValue::EntityLink { .. }
                     | PropValue::ParamRow { .. }
-                    | PropValue::ParamAddRow => return None,
+                    | PropValue::ParamAddRow
+                    | PropValue::ParamsVisibilityToggle(_) => return None,
                 })
             }
         }