refactor: rename "folder" to "package" throughout codebase

- Rename CSS files: _card-folder.scss → card-package
- Rename template files: _folder.scss → package
- Update all CSS class names and selectors
- Delete old folder blueprints and templates
- Add new package blueprints with improved structure
- Update investigation-summary template and blueprint
- Add "Dossiers" menu item in panel configuration
- Improve package blueprint with linkedContent field

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

site/blueprints/pages/investigation-summary.yml

@@ -88,7 +88,7 @@ tabs:
     label: Métadonnées
     icon: table
     fields:
-      folder:
+      package:
         label: Dossier
         type: select
         options: query