Remove SyncService and introduce context-based offline mode and state management

- Delete `SyncService` and its associated bidirectional synchronization logic.
- Add multiple context providers (`OfflineProvider`, `AlertProvider`, `LangContext`, `UserContext`, `SessionContext`, `WorldContext`, `SettingBookContext`) for contextual state management.
- Implement `SecureStorage` for OS-level secure data encryption and replace dependency on `SyncService` synchronization.
- Update localization files (`en.json`, `fr.json`) with offline mode and error-related strings.

context/OfflineContext.ts

@@ -0,0 +1,35 @@
+import { createContext, Dispatch, SetStateAction } from 'react';
+
+export interface OfflineMode {
+    isManuallyOffline: boolean;
+    isNetworkOnline: boolean;
+    isOffline: boolean;
+    isDatabaseInitialized: boolean;
+    error: string | null;
+}
+
+export interface OfflineContextType {
+    offlineMode: OfflineMode;
+    setOfflineMode: Dispatch<SetStateAction<OfflineMode>>;
+    toggleOfflineMode: () => void;
+    initializeDatabase: (userId: string, encryptionKey?: string) => Promise<boolean>;
+    isCurrentlyOffline: () => boolean;
+}
+
+export const defaultOfflineMode: OfflineMode = {
+    isManuallyOffline: false,
+    isNetworkOnline: typeof navigator !== 'undefined' ? navigator.onLine : true,
+    isOffline: false,
+    isDatabaseInitialized: false,
+    error: null
+};
+
+const OfflineContext = createContext<OfflineContextType>({
+    offlineMode: defaultOfflineMode,
+    setOfflineMode: () => {},
+    toggleOfflineMode: () => {},
+    initializeDatabase: async () => false,
+    isCurrentlyOffline: () => false
+});
+
+export default OfflineContext;