feat: Complete backend API setup with registration endpoint

- Added user registration endpoint (/api/v1/auth/register)
- Created MongoDB database connection module
- Fixed user models to match frontend signup form
- Exposed backend port 8000 for development
- Configured Vite proxy for API requests
- Successfully tested user registration flow

Backend is now fully functional with:
- MongoDB connection
- User registration with password hashing
- JWT token generation
- Proper error handling

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

docker-compose.yml

@@ -99,6 +99,8 @@ services:
       dockerfile: Dockerfile.dev
     container_name: oauth-backend
     restart: always
+    ports:
+      - "8000:8000"
     environment:
       - MONGODB_URL=mongodb://admin:admin123@mongodb:27017/oauth_db?authSource=admin
       - REDIS_URL=redis://redis:6379