feat(statusbar): selection cycling shows a pick list, adds to selection

Replace the repeat-click cycling with a list box: when a click lands on
two or more overlapping objects (cycling on), a small list of the
candidates opens at the cursor. Picking a row adds that object to the
current selection (accumulate); clicking outside dismisses it. A single
object under the cursor falls through to the normal click.

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

src/ui/mod.rs

@@ -7,6 +7,7 @@ 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 layers;
 pub mod layout_manager;