fix(mleader): use lineweight choices

Replace the raw sentinel input with typed CAD lineweight options so special
values display correctly and unsupported values cannot be entered.

Refs #522

src/app/view/modal.rs

@@ -393,7 +393,6 @@ impl OpenCADStudio {
                         line_color: &self.mls_line_color,
                         text_color: &self.mls_text_color,
                         description: &self.mls_description,
-                        line_weight: &self.mls_line_weight,
                         align_space: &self.mls_align_space,
                         block_color: &self.mls_block_color,
                         block_rotation: &self.mls_block_rotation,