feat: enhance welcome email sending by using DEFAULT_FROM_EMAIL if available

fix: standardize Authorization header formatting in email sending function

feat: enhance email sending functionality with customizable From header and display name

feat: enable CORS support in the API router

fix: update Redis initialization to handle missing environment variable and connection errors

fix: update route destination in vercel.json to point to main.go

feat: Update README and restructure API package

Update README.md

feat: Modified content

feat: Add new documentation

add presentation html new

add presentation html

add presentation

test 13

test 12