Feat: Add email authentication and user insertion to Supabase DB

[zaineel]

🚀 Feature: Supabase Authentication (#14)

✅ Summary

This PR adds email-based authentication using Supabase and stores authenticated users in the Supabase database.

📋 Changes Implemented

• Configured Supabase client
• Implemented email sign-up and sign-in flow
• On successful authentication, user is added to the Supabase users table (if not already present)

🧪 How to Test

1. Go to the login/register screen
2. Sign up with an email and password
3. Check the Supabase dashboard to verify a new user entry is created in the users table

🔗 Related Issue

Closes #14

📎 Notes

• Make sure .env contains correct Supabase URL and anon/public key
• Let me know if you'd like changes or if we should add error/success UI next

[zaineel]

updated the Expo SDK to the latest