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/keyManager.ts

@@ -1,33 +1,35 @@
-import Store from 'electron-store';
+import { getSecureStorage } from '../storage/SecureStorage.js';
 
 /**
- * Key Manager - Manages user encryption keys stored in electron-store
+ * Key Manager - Manages user encryption keys using OS-level secure storage
+ * - macOS: Keychain
+ * - Windows: DPAPI
+ * - Linux: gnome-libsecret/kwallet
  */
 
-const store = new Store({
-    encryptionKey: 'eritors-scribe-secure-key'
-});
-
 /**
- * Get user encryption key from secure store
+ * Get user encryption key from secure storage
  * @param userId - User ID
- * @returns User's encryption key or null if not found
+ * @returns User's encryption key
+ * @throws Error if encryption key not found
  */
 export function getUserEncryptionKey(userId: string): string {
-    const key: string | undefined = store.get(`encryptionKey-${userId}`) as string | undefined;
-    if (key === undefined) {
+    const storage = getSecureStorage();
+    const key = storage.get<string>(`encryptionKey-${userId}`);
+    if (key === null || key === undefined) {
         throw new Error(`Unknown encryptionKey`);
     }
     return key;
 }
 
 /**
- * Set user encryption key in secure store
+ * Set user encryption key in secure storage (OS-encrypted)
  * @param userId - User ID
  * @param encryptionKey - Encryption key to store
  */
 export function setUserEncryptionKey(userId: string, encryptionKey: string): void {
-    store.set(`encryptionKey-${userId}`, encryptionKey);
+    const storage = getSecureStorage();
+    storage.set(`encryptionKey-${userId}`, encryptionKey);
 }
 
 /**
@@ -36,7 +38,8 @@ export function setUserEncryptionKey(userId: string, encryptionKey: string): voi
  * @returns True if key exists
  */
 export function hasUserEncryptionKey(userId: string): boolean {
-    return store.has(`encryptionKey-${userId}`);
+    const storage = getSecureStorage();
+    return storage.has(`encryptionKey-${userId}`);
 }
 
 /**
@@ -44,5 +47,6 @@ export function hasUserEncryptionKey(userId: string): boolean {
  * @param userId - User ID
  */
 export function deleteUserEncryptionKey(userId: string): void {
-    store.delete(`encryptionKey-${userId}`);
+    const storage = getSecureStorage();
+    storage.delete(`encryptionKey-${userId}`);
 }