Add openExternal IPC handler and integrate with UI components

- Introduce `openExternal` IPC handler in `electron/main.ts` for opening external links via the default browser or native app.
- Update typings in `electron.d.ts` and `preload.ts` to include `openExternal`.
- Refactor `ComposerRightBar` and `LeftBar` components to leverage `electron.openExternal` for external link actions (e.g., Facebook, Discord).
- Add offline mode logic to filter navigation options in `ComposerRightBar` and `LeftBar`.
- Enhance footer bar to display book titles when chapters are unavailable.

electron/main.ts

@@ -1,4 +1,4 @@
-import {app, BrowserWindow, ipcMain, nativeImage, protocol, safeStorage} from 'electron';
+import {app, BrowserWindow, ipcMain, nativeImage, protocol, safeStorage, shell} from 'electron';
 import * as path from 'path';
 import {fileURLToPath} from 'url';
 import * as fs from 'fs';
@@ -116,6 +116,11 @@ function createMainWindow(): void {
   });
 }
 
+// IPC Handler pour ouvrir des liens externes (navigateur/app native)
+ipcMain.handle('open-external', async (_event, url: string) => {
+  await shell.openExternal(url);
+});
+
 // IPC Handlers pour la gestion du token (OS-encrypted storage)
 ipcMain.handle('get-token', () => {
   const storage:SecureStorage = getSecureStorage();