Function printBanner

Displays the IGCv3 ASCII banner. Colors: {B} -> Bright Black (Gray) {F} -> Green {F2} -> Red {R} -> Reset

Respects environment variables:

• CI=true : Suppresses both banner and clear (for CI/CD)
• IGC_NO_BANNER=1 : Suppresses banner only
• IGC_NO_CLEAR=1 : Suppresses clear only