Add async-safe polyfills, Jest custom config, and improved token validation

- Introduced Web Crypto API polyfills (`@peculiar/webcrypto`) for Node.js to enable SSR-safe cryptography utilities.
- Added Jest setup file for global mocks (e.g., `localStorage`, `sessionStorage`, and `TextEncoder/Decoder`).
- Enhanced token validation behavior in `storage` tests to reject incomplete tokens.
- Replaced runtime configuration validation with clamping using `parseIntSafe` constraints for improved reliability.
- Updated `package.json` and `package-lock.json` to include new dependencies (`@peculiar/webcrypto` and related libraries).

frontend/jest.setup.js

@@ -0,0 +1,86 @@
+// Learn more: https://github.com/testing-library/jest-dom
+import '@testing-library/jest-dom'
+import { Crypto } from '@peculiar/webcrypto';
+
+// Mock window object
+global.window = global.window || {};
+
+// Use real Web Crypto API polyfill for Node environment
+const cryptoPolyfill = new Crypto();
+
+// Store references before assignment
+const subtleRef = cryptoPolyfill.subtle;
+const getRandomValuesRef = cryptoPolyfill.getRandomValues.bind(cryptoPolyfill);
+
+// Use Object.defineProperty to ensure properties aren't overridden
+if (!global.crypto) {
+  global.crypto = {};
+}
+
+Object.defineProperty(global.crypto, 'subtle', {
+  value: subtleRef,
+  writable: false,
+  configurable: true,
+  enumerable: true,
+});
+
+Object.defineProperty(global.crypto, 'getRandomValues', {
+  value: getRandomValuesRef,
+  writable: false,
+  configurable: true,
+  enumerable: true,
+});
+
+// Mock TextEncoder/TextDecoder if not available
+if (typeof TextEncoder === 'undefined') {
+  global.TextEncoder = class TextEncoder {
+    encode(str) {
+      const buf = Buffer.from(str, 'utf-8');
+      return new Uint8Array(buf);
+    }
+  };
+}
+
+if (typeof TextDecoder === 'undefined') {
+  global.TextDecoder = class TextDecoder {
+    decode(arr) {
+      return Buffer.from(arr).toString('utf-8');
+    }
+  };
+}
+
+// Mock localStorage (must be on global to satisfy typeof checks)
+global.localStorage = {
+  getItem: jest.fn(),
+  setItem: jest.fn(),
+  removeItem: jest.fn(),
+  clear: jest.fn(),
+  length: 0,
+  key: jest.fn(),
+};
+
+// Mock sessionStorage (must be on global to satisfy typeof checks)
+global.sessionStorage = {
+  getItem: jest.fn(),
+  setItem: jest.fn(),
+  removeItem: jest.fn(),
+  clear: jest.fn(),
+  length: 0,
+  key: jest.fn(),
+};
+
+// Reset storage mocks before each test
+beforeEach(() => {
+  // Don't use clearAllMocks - it breaks the mocks
+  // Instead reset individual storage mock return values
+  if (global.localStorage && typeof global.localStorage.getItem.mockReset === 'function') {
+    global.localStorage.getItem.mockReset().mockReturnValue(null);
+    global.localStorage.setItem.mockReset();
+    global.localStorage.removeItem.mockReset();
+  }
+  if (global.sessionStorage && typeof global.sessionStorage.getItem.mockReset === 'function') {
+    global.sessionStorage.getItem.mockReset().mockReturnValue(null);
+    global.sessionStorage.setItem.mockReset();
+    global.sessionStorage.removeItem.mockReset();
+  }
+});