Fix token validation to support both sgu_ and sgo_ prefixes - #40

sg-cli only accepted sgu_ (personal) tokens, rejecting valid sgo_ (organization) tokens.

• Updated the token prefix check to accept both sgu_ and sgo_ prefixes
• Updated the error message to clarify both token types are supported

# Before
if [ -z "${API_TOKEN}" ] || [ "sgu_" != "${API_TOKEN:0:4}" ]; then

# After
if [ -z "${API_TOKEN}" ] || { [ "${API_TOKEN:0:4}" != "sgu_" ] && [ "${API_TOKEN:0:4}" != "sgo_" ]; }; then