feat(styles): unify the five style managers behind a shared frame

The text/dimension/table/multileader/multiline managers were hand-copied,
so their list CRUD kept drifting and breaking: Dimension's New created
nothing (#73), new text styles never reached the ribbon dropdown (#74),
and several were added with a NULL handle (dropped on DWG save, #67).

Collapse the duplicated parts into three shared pieces and leave only the
per-manager property editor bespoke:

- app/style_ops.rs: one StyleKind-dispatched CRUD layer (new / copy /
  delete / rename) handling handle allocation, ribbon sync, Table re-key
  and name-reference rewrites in a single place.
- ui/style_manager.rs: the window scaffold — uniform toolbar (New / Copy /
  Delete on the left, Set Current + Apply on the right), style list and
  chrome. Each manager now only builds its editor.
- ui/style_list.rs: the list row — single click selects, double click
  starts an inline rename.

New capabilities, now consistent across all five:
- Copy duplicates the selected style.
- Double-click a name to rename it inline.
- Right side is always Set Current + Apply (added Table set-current;
  MLine apply is a documented placeholder until its editor is editable).

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

src/ui/mod.rs

@@ -4,11 +4,10 @@ pub const ROW_H: f32 = 26.0;
 
 pub mod about;
 pub mod app_menu;
-pub mod isolate_popup;
-pub mod update_notice;
 pub mod command_line;
 pub mod cycle_popup;
 pub mod dimstyle;
+pub mod isolate_popup;
 pub mod layers;
 pub mod layout_manager;
 pub mod mleaderstyle;
@@ -26,10 +25,13 @@ pub mod snap_popup;
 pub mod statusbar;
 pub mod statusbar_config;
 pub mod statusbar_menu;
+pub mod style_list;
+pub mod style_manager;
 pub mod tablestyle;
 pub mod text_util;
 pub mod textstyle;
 pub mod units_popup;
+pub mod update_notice;
 
 pub use app_menu::AppMenu;
 pub use command_line::CommandLine;