Refactor imports, streamline database IPC handlers, and improve offline support

- Replace absolute import paths with relative paths for consistency across files.
- Transition database operations in Electron main process to modular handlers in `ipc/book.ipc.ts` using the `createHandler` pattern.
- Update database sync service to use `window.electron.invoke()` for improved reliability and structure.
- Refactor `AddNewBookForm` to handle both online and offline book creation seamlessly.

electron/main.ts

@@ -222,192 +222,8 @@ ipcMain.handle('db-initialize', (_event, userId: string, encryptionKey: string)
   }
 });
 
-/**
- * Get all books
- */
-ipcMain.handle('db-get-books', () => {
-  try {
-    const db = getDatabaseService();
-    const books = db.getBooks();
-    return { success: true, data: books };
-  } catch (error) {
-    console.error('Failed to get books:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Get single book with all data
- */
-ipcMain.handle('db-get-book', (_event, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    const book = db.getBook(bookId);
-    return { success: true, data: book };
-  } catch (error) {
-    console.error('Failed to get book:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Save book
- */
-ipcMain.handle('db-save-book', (_event, book: any, authorId?: string) => {
-  try {
-    const db = getDatabaseService();
-    db.saveBook(book, authorId);
-    return { success: true };
-  } catch (error) {
-    console.error('Failed to save book:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Delete book
- */
-ipcMain.handle('db-delete-book', (_event, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    db.deleteBook(bookId);
-    return { success: true };
-  } catch (error) {
-    console.error('Failed to delete book:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Save chapter
- */
-ipcMain.handle('db-save-chapter', (_event, chapter: any, bookId: string, contentId?: string) => {
-  try {
-    const db = getDatabaseService();
-    db.saveChapter(chapter, bookId, contentId);
-    return { success: true };
-  } catch (error) {
-    console.error('Failed to save chapter:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Get characters for a book
- */
-ipcMain.handle('db-get-characters', (_event, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    const characters = db.getCharacters(bookId);
-    return { success: true, data: characters };
-  } catch (error) {
-    console.error('Failed to get characters:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Save character
- */
-ipcMain.handle('db-save-character', (_event, character: any, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    db.saveCharacter(character, bookId);
-    return { success: true };
-  } catch (error) {
-    console.error('Failed to save character:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Get AI conversations for a book
- */
-ipcMain.handle('db-get-conversations', (_event, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    const conversations = db.getConversations(bookId);
-    return { success: true, data: conversations };
-  } catch (error) {
-    console.error('Failed to get conversations:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Save AI conversation
- */
-ipcMain.handle('db-save-conversation', (_event, conversation: any, bookId: string) => {
-  try {
-    const db = getDatabaseService();
-    db.saveConversation(conversation, bookId);
-    return { success: true };
-  } catch (error) {
-    console.error('Failed to save conversation:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Get sync status
- */
-ipcMain.handle('db-get-sync-status', () => {
-  try {
-    const db = getDatabaseService();
-    const status = db.getSyncStatus();
-    return { success: true, data: status };
-  } catch (error) {
-    console.error('Failed to get sync status:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
-
-/**
- * Get pending changes
- */
-ipcMain.handle('db-get-pending-changes', (_event, limit: number = 100) => {
-  try {
-    const db = getDatabaseService();
-    const changes = db.getPendingChanges(limit);
-    return { success: true, data: changes };
-  } catch (error) {
-    console.error('Failed to get pending changes:', error);
-    return {
-      success: false,
-      error: error instanceof Error ? error.message : 'Unknown error'
-    };
-  }
-});
+// NOTE: All database IPC handlers have been moved to ./ipc/book.ipc.ts
+// and use the new createHandler() pattern with auto userId/lang injection
 
 app.whenReady().then(() => {
   console.log('App ready, isDev:', isDev);