Refactor: create shared entity-item base, remove duplicate CSS

- Add _entity-item.scss shared component for chips and list items
- Refactor _list-preview.scss to use shared patterns
- Delete entity-list-preview.css (duplicate hardcoded styles)
- All preview styling now comes from SCSS build only

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

sources/scss/main.scss

@@ -16,6 +16,7 @@
 
 // Components
 @use 'components/entity-selector';
+@use 'components/entity-item';  // Shared base for chips and list items
 @use 'components/dropdown';
 @use 'components/chips';
 @use 'components/groups';