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/preload.ts

@@ -12,4 +12,21 @@ contextBridge.exposeInMainWorld('electron', {
   // Auth events
   loginSuccess: (token: string) => ipcRenderer.send('login-success', token),
   logout: () => ipcRenderer.send('logout'),
+
+  // Database operations
+  generateEncryptionKey: (userId: string) => ipcRenderer.invoke('generate-encryption-key', userId),
+  getUserEncryptionKey: (userId: string) => ipcRenderer.invoke('get-user-encryption-key', userId),
+  setUserEncryptionKey: (userId: string, encryptionKey: string) => ipcRenderer.invoke('set-user-encryption-key', userId, encryptionKey),
+  dbInitialize: (userId: string, encryptionKey: string) => ipcRenderer.invoke('db-initialize', userId, encryptionKey),
+  dbGetBooks: () => ipcRenderer.invoke('db-get-books'),
+  dbGetBook: (bookId: string) => ipcRenderer.invoke('db-get-book', bookId),
+  dbSaveBook: (book: any, authorId?: string) => ipcRenderer.invoke('db-save-book', book, authorId),
+  dbDeleteBook: (bookId: string) => ipcRenderer.invoke('db-delete-book', bookId),
+  dbSaveChapter: (chapter: any, bookId: string, contentId?: string) => ipcRenderer.invoke('db-save-chapter', chapter, bookId, contentId),
+  dbGetCharacters: (bookId: string) => ipcRenderer.invoke('db-get-characters', bookId),
+  dbSaveCharacter: (character: any, bookId: string) => ipcRenderer.invoke('db-save-character', character, bookId),
+  dbGetConversations: (bookId: string) => ipcRenderer.invoke('db-get-conversations', bookId),
+  dbSaveConversation: (conversation: any, bookId: string) => ipcRenderer.invoke('db-save-conversation', conversation, bookId),
+  dbGetSyncStatus: () => ipcRenderer.invoke('db-get-sync-status'),
+  dbGetPendingChanges: (limit?: number) => ipcRenderer.invoke('db-get-pending-changes', limit),
 });