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/packages.yml

@@ -0,0 +1,19 @@
+title: Dossiers
+
+tabs:
+  contentTab:
+    label: Contenu
+    sections:
+      packages:
+        label: Dossiers
+        type: pages
+        text: "{{ page.title }}"
+        info: "{{ page.linkedContent.toPages.count }} contenus"
+        layout: cards
+        size: huge
+        search: true
+        image:
+          cover: true
+          ratio: 12/7
+        template: package
+  seo: seo/page