Add "Login with Google" Authentication Option

[vikas-saini-7]

Description

Implement a "Login with Google" authentication option in the Code Collab platform using NextAuth.js with the Google provider.

Why is this feature useful?

• Simplifies the login experience by allowing users to sign in with their Google accounts.
• Increases trust and reduces friction for new users joining the platform.
• Widely expected feature in modern web apps.

How could it work?

• Use the next-auth package, which is already set up in the project.
• Add Google provider to authOptions in the NextAuth config file.
• Use "Continue with Google" button which is already been added in UI.
• Ensure that user session and database entries are created correctly upon first login.

Screenshots or UI idea (if applicable)

![Image](https://github.com/user-attachments/assets/49887494-654d-48e9-9776-ac6881b090f

Use Tailwind + Shadcn.

Additional Information

• You'll need to create OAuth credentials in the Google Cloud Console.
• The following environment variables will be required (add to .env.example too):

GOOGLE_CLIENT_ID=your-google-client-id
GOOGLE_CLIENT_SECRET=your-google-client-secret