feat(statusbar): isolate action menu on the pill and right-click

Clicking the ISO pill now opens a small menu with Isolate Objects, Hide
Objects and End Isolation instead of ending isolation directly; rows
that don't apply (no selection / nothing hidden) are dimmed. The same
actions are added to the viewport right-click menu.

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

src/ui/mod.rs

@@ -4,6 +4,7 @@ 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 dimstyle;