fix: resolve GitHub OAuth redirect failure

[Shanidhya01]

Summary

Fixes the GitHub OAuth authentication issue where users were redirected back to the sign-in page with error=github instead of being successfully authenticated and taken to the dashboard.

Closes #1221

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor / code cleanup

Changes Made

• Fixed GitHub OAuth authentication flow configuration
• Corrected redirect/callback handling after successful login
• Improved environment variable handling for production deployment
• Added better error handling/logging for OAuth authentication failures
• Verified compatibility between local and Vercel deployment environments

How to Test

Steps for the reviewer to verify this works:

1. Run the application locally with valid GitHub OAuth credentials
2. Navigate to the sign-in page
3. Click Sign in with GitHub
4. Complete GitHub authorization flow
5. Confirm successful redirect to /dashboard
6. Verify no redirect loop occurs with error=github
7. Test deployed preview build to confirm production auth flow works

N/A (Authentication bug fix)

Checklist

• Linked issue in summary
• npm run lint passes locally
• No TypeScript errors (npm run type-check)
• Self-reviewed the diff
• Added/updated tests if applicable

[vercel]

@Shanidhya01 is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[github-actions]

GSSoC Label Checklist 🏷️

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