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/package.yml

@@ -0,0 +1,26 @@
+title: Dossier
+
+tabs:
+  contentTab:
+    label: Contenu
+    icon: page
+    fields:
+      cover:
+        label: Visuel de couverture
+        type: files
+        multiple: false
+        layout: cards
+        width: 1/3
+        image:
+          ratio: 12/7
+          cover: true
+        help: Image utilisée dans la liste des dossiers
+      description:
+        label: Description
+        type: writer
+        width: 2/3
+      linkedContent:
+        label: Contenu
+        type: pages
+        query: site.find('enquetes').children
+  seo: seo/page