feat(mleaderstyle): add Multileader Style editor window

New dedicated style-manager window for MultiLeaderStyle objects (the
existing mlstyle window edits MLineStyle, not multileader). Opened via
the MLEADERSTYLE command / ribbon manager entry.

Editable across Leader Format / Structure / Content sections:
- path/content/text-angle/text-alignment enums (cycle buttons)
- line & text color (ACI), arrowhead & break-gap sizes
- landing distance/gap, max points, segment angles, scale factor
- default text, text height
- enable landing/dogleg, text frame, text-always-left, annotative
New/Delete/Set-Current style management.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/commands.rs

@@ -3983,7 +3983,10 @@ impl OpenCADStudio {
                 let parts: Vec<&str> = raw_rest.split_whitespace().collect();
                 let sub = parts.first().map(|s| s.to_uppercase()).unwrap_or_default();
                 match sub.as_str() {
-                    "" | "LIST" | "?" => {
+                    "" | "DIALOG" | "UI" => {
+                        return Task::done(Message::MLeaderStyleDialogOpen);
+                    }
+                    "LIST" | "?" => {
                         let styles: Vec<String> = self.tabs[i]
                             .scene
                             .document