Migrate from electron-store to OS-level secure storage (getSecureStorage)

- Replace `electron-store` with OS-level encrypted storage for secure token, userId, and language management in `LocalSystem` and `keyManager`.
- Add `init-user` IPC handler to initialize user data and manage encryption keys.
- Update login process to handle encrypted storage saving with fallback for macOS issues.
- Add offline warning component to `login/page.tsx` to handle first-time sync requirements.
- Remove `electron-store` and associated dependencies from `package.json` and `package-lock.json`.

electron/database/LocalSystem.ts

@@ -1,33 +1,26 @@
 import type { IpcMainInvokeEvent } from 'electron';
-import Store from 'electron-store';
+import { getSecureStorage } from '../storage/SecureStorage.js';
 
 // ============================================================
 // SESSION MANAGEMENT - Auto-inject userId and lang
 // ============================================================
 
 /**
- * Electron store instance for session management
- * - userId: Set during login via 'login-success' event
- * - userLang: Set via 'set-lang' handler
- */
-const store = new Store({
-    encryptionKey: 'eritors-scribe-secure-key'
-});
-
-/**
- * Get userId from electron-store
+ * Get userId from secure storage (OS-encrypted)
  * Set during login via 'login-success' event
  */
 function getUserIdFromSession(): string | null {
-    return store.get('userId', null) as string | null;
+    const storage = getSecureStorage();
+    return storage.get<string>('userId', null);
 }
 
 /**
- * Get lang from electron-store
+ * Get lang from secure storage
  * Set via 'set-lang' handler, defaults to 'fr'
  */
 function getLangFromSession(): 'fr' | 'en' {
-    return store.get('userLang', 'fr') as 'fr' | 'en';
+    const storage = getSecureStorage();
+    return storage.get<'fr' | 'en'>('userLang', 'fr') as 'fr' | 'en';
 }
 
 // ============================================================