Introduce local fallback for book creation and improve error handling

- Added support for creating books locally when the cloud limit is reached.
- Enhanced error handling in `AddNewBookForm` with `ApiError` and fallback logic for local book creation.
- Implemented `BookTypeLimit` to manage type-specific book limits with visual indicators in `BookList`.
- Refactored `TombstoneRecord` to standardize naming conventions for better API compatibility.
- Updated `useSyncSeries` and `useSyncBooks` to handle empty tombstones gracefully.
- Updated locales with new translations for fallback and error messaging.

lib/api/client.ts

@@ -13,10 +13,20 @@ interface ApiRequestConfig {
     contentType?: ContentType;
 }
 
+export class ApiError extends Error {
+    statusCode: number;
+    constructor(message: string, statusCode: number) {
+        super(message);
+        this.statusCode = statusCode;
+        this.name = 'ApiError';
+    }
+}
+
 function handleApiError(error: unknown): never {
     if (axios.isAxiosError(error)) {
         const serverMessage: string = error.response?.data?.message || error.response?.data || error.message;
-        throw new Error(serverMessage);
+        const statusCode: number = error.response?.status ?? 500;
+        throw new ApiError(serverMessage, statusCode);
     } else if (error instanceof Error) {
         throw new Error(error.message);
     }

lib/locales/en.json

@@ -718,7 +718,10 @@
       "titleTooShort": "Title is too short. Minimum 2 characters required.",
       "titleTooLong": "Title is too long. Maximum 50 characters allowed.",
       "typeMissing": "Select a genre.",
-      "addingBook": "An error occurred while adding the book."
+      "addingBook": "An error occurred while adding the book.",
+      "limitReached": "You have reached the book limit for this type on the cloud.",
+      "saveLocally": "Save locally",
+      "localFallbackDescription": "You can still save this book locally on your device."
     },
     "bookTypeHint": {
       "title": "Type of work",

lib/locales/fr.json

@@ -717,7 +717,10 @@
       "titleTooShort": "Le titre est trop court. Minimum 2 caractères requis",
       "titleTooLong": "Le titre est trop long. Maximum 50 caractères autorisés",
       "typeMissing": "Sélectionner un genre.",
-      "addingBook": "Une erreur est survenue lors de l'ajout du livre."
+      "addingBook": "Une erreur est survenue lors de l'ajout du livre.",
+      "limitReached": "Vous avez atteint la limite de livres pour ce type sur le cloud.",
+      "saveLocally": "Sauvegarder localement",
+      "localFallbackDescription": "Vous pouvez tout de même enregistrer ce livre localement sur votre appareil."
     },
     "bookTypeHint": {
       "title": "Type d'oeuvre",

lib/tauri.ts

@@ -44,10 +44,10 @@ export interface SyncCheckResult {
 }
 
 export interface TombstoneRecord {
-    tableName: string;
-    entityId: string;
-    bookId: string | null;
-    deletedAt: number;
+    table_name: string;
+    entity_id: string;
+    book_id: string | null;
+    deleted_at: number;
 }
 
 // ─── User & Auth ───────────────────────────────────────────

lib/types/book.ts

@@ -106,3 +106,8 @@ export interface BookTags {
     objects: Tag[];
     worldElements: Tag[];
 }
+
+export interface BookTypeLimit {
+    current: number;
+    max: number;
+}