Implement Google OAuth flow and enhance login functionality

- Updated the Google Sign-In integration to utilize the new OAuth callback mechanism.
- Added a redirect flow for Google authentication, improving user experience.
- Enhanced error handling and user feedback during the login process.
- Removed hardcoded Google client ID in favor of environment variable usage.
- Introduced a new component for handling OAuth callbacks and updated the App component to manage authentication states accordingly.
- Improved API route for processing OAuth callbacks, including token exchange and user verification.

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "dev": "concurrently \"npm run dev:frontend\" \"npm run dev:backend\"",
     "dev:frontend": "webpack serve --mode development --config webpack.config.js",
-    "dev:backend": "nodemon src/index.js",
+    "dev:backend": "nodemon --exitcrash src/index.js",
     "build": "webpack --config webpack.prod.config.js",
     "build:prod": "npm run build && npm run start:prod",
     "start": "npm run build && node src/index.js",