Set up environment variables for the project using Vercel CLI. 

Task: Add these environment variables to the Vercel project:
- Production environment variable: API_URL = https://api.example.com  
- Development environment variable: DEBUG = true

Success criteria:
- Use `vercel env` command to add the variables
- Verify the variables were actually added by listing them with `vercel env ls`
- Do NOT just create local .env files - the variables must be added to the Vercel platform
- If you encounter permission issues or authentication problems, report this as a failure

Important: Only report success if you can confirm the environment variables are visible in the Vercel platform.