Remove unused components and models for improved maintainability

- Deleted redundant components (`AddActionButton`, `AlertBox`, `AlertStack`, `BackButton`, `CancelButton`, and `CollapsableArea`) and related files.
- Removed unused models (`Book`, `BookSerie`, `BookTables`, `Character`, and `Chapter`) to reduce codebase clutter.
- Updated project structure and references to reflect these removals.

lib/constants/user.ts

@@ -0,0 +1,8 @@
+import {SelectBoxProps} from "@/components/form/SelectBox";
+
+export const writingLevel: SelectBoxProps[] = [
+    {value: '0', label: 'Sélectionner un niveau d\'écriture'},
+    {value: '1', label: 'Je suis débutant'},
+    {value: '2', label: 'Je suis intermédiaire'},
+    {value: '3', label: 'Je suis avancé'},
+];