feat: Add Google & GitHub Authentication and fix backend stability issues

[Dev1822]

Closes #357

Overview

This PR introduces third-party OAuth support by integrating both Google and GitHub authentication into the Sign-In and Sign-Up flows. It also resolves a series of critical backend syntax errors and misconfigurations that were causing the server to crash on startup.

Key Changes

🌟 Features

• Google Authentication: Integrated @react-oauth/google to allow users to sign up and log in using their Google accounts.
• GitHub Authentication: Built a custom OAuth callback flow to exchange GitHub authorization codes for access tokens.

🐛 Bug Fixes

• Backend Server Crashes: Repaired severely corrupted files (server.js, socket.js, registrationRoutes.js, etc.) by fixing syntax errors and resolving undefined variable references.
• Database Connection: Uncommented the connectDB() initialization in server.js.
• React StrictMode Bug: Implemented useRef flags to prevent React 18's StrictMode from executing the GitHub OAuth callback twice.

Testing Steps

To verify these changes, reviewers should follow these steps:

1. Ensure the following environment variables are set in .env for the backend: GOOGLE_CLIENT_ID, GITHUB_CLIENT_ID, and GITHUB_CLIENT_SECRET.
2. Ensure the following environment variables are set in .env for the frontend: VITE_GOOGLE_CLIENT_ID, VITE_GITHUB_CLIENT_ID.
3. Start both the frontend and backend servers.
4. Navigate to /signup and attempt to create an account via the "Continue with Google" button. Verify successful redirection and account creation.
5. Navigate to /login and attempt to sign in via the "Continue with GitHub" button. Verify successful sign-in.

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[Dev1822]

Hello @anubhavxdev , It has been 4 days since I have created this PR. Kindly give me any update on this or suggest me any changes if needed.