Integrate local database management and IPC handlers into Electron

- Add comprehensive IPC handlers for database operations like books, chapters, characters, and conversations.
- Implement local database initialization and user data encryption.
- Update preload script paths for consistent environment handling.
- Modify `page.tsx` to initialize local database within Electron environment.
- Add new dependencies including `node-sqlite3-wasm` and `electron-rebuild`.

electron.d.ts

@@ -5,6 +5,23 @@ export interface IElectronAPI {
   removeToken: () => Promise<boolean>;
   loginSuccess: (token: string) => void;
   logout: () => void;
+
+  // Database operations
+  generateEncryptionKey: (userId: string) => Promise<{ success: boolean; key?: string; error?: string }>;
+  getUserEncryptionKey: (userId: string) => Promise<string | null>;
+  setUserEncryptionKey: (userId: string, encryptionKey: string) => Promise<boolean>;
+  dbInitialize: (userId: string, encryptionKey: string) => Promise<{ success: boolean; error?: string }>;
+  dbGetBooks: () => Promise<{ success: boolean; data?: any[]; error?: string }>;
+  dbGetBook: (bookId: string) => Promise<{ success: boolean; data?: any; error?: string }>;
+  dbSaveBook: (book: any, authorId?: string) => Promise<{ success: boolean; error?: string }>;
+  dbDeleteBook: (bookId: string) => Promise<{ success: boolean; error?: string }>;
+  dbSaveChapter: (chapter: any, bookId: string, contentId?: string) => Promise<{ success: boolean; error?: string }>;
+  dbGetCharacters: (bookId: string) => Promise<{ success: boolean; data?: any[]; error?: string }>;
+  dbSaveCharacter: (character: any, bookId: string) => Promise<{ success: boolean; error?: string }>;
+  dbGetConversations: (bookId: string) => Promise<{ success: boolean; data?: any[]; error?: string }>;
+  dbSaveConversation: (conversation: any, bookId: string) => Promise<{ success: boolean; error?: string }>;
+  dbGetSyncStatus: () => Promise<{ success: boolean; data?: any[]; error?: string }>;
+  dbGetPendingChanges: (limit?: number) => Promise<{ success: boolean; data?: any[]; error?: string }>;
 }
 
 declare global {