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/package.json

@@ -52,6 +52,7 @@
   "devDependencies": {
     "@eslint/eslintrc": "^3",
     "@hey-api/openapi-ts": "^0.86.11",
+    "@peculiar/webcrypto": "^1.5.0",
     "@playwright/test": "^1.56.1",
     "@tailwindcss/postcss": "^4",
     "@testing-library/jest-dom": "^6.9.1",