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/ui/mod.rs

@@ -9,6 +9,7 @@ pub mod command_line;
 pub mod dimstyle;
 pub mod layers;
 pub mod layout_manager;
+pub mod mleaderstyle;
 pub mod mlstyle;
 pub mod open_progress;
 pub mod overlay;