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/utils/user.ts

@@ -0,0 +1,44 @@
+import {GuideTour, Subscription, UserProps} from "@/lib/types/user";
+import {SessionProps} from "@/lib/types/session";
+
+export function getCurrentSubscription(user: UserProps | null, type: "quill-sense" | "use-your-keys" | "quill-trial"): Subscription | null {
+    if (!user || !user.subscription || user.subscription.length === 0) {
+        return null;
+    }
+    return user.subscription.find((sub: Subscription): boolean => {
+        return sub.subType === type && sub.status;
+    }) || null;
+}
+
+export function getWritingLevel(level: number): string {
+    switch (level) {
+        case 1:
+            return 'Débutant';
+        case 2:
+            return 'Intermédiaire';
+        case 3:
+            return 'Avancé';
+        default:
+            return 'Débutant';
+    }
+}
+
+export function guideTourDone(guide: GuideTour[], tour: string): boolean {
+    if (!guide || !tour) return false;
+    return guide.find((guide: GuideTour): boolean => guide[tour]) === undefined;
+}
+
+export function setNewGuideTour(session: SessionProps, tour: string): SessionProps {
+    if (!session.user) return session;
+    const newGuideTour: GuideTour[] = [
+        ...(session.user.guideTour ?? []),
+        {[tour]: true}
+    ];
+    return {
+        ...session,
+        user: {
+            ...session.user,
+            guideTour: newGuideTour
+        }
+    };
+}