I've never heard of a no jeans policy except in the dining room at dinner time.
I don't pack jeans because they take up more space than khakis and they don't feature elastic in the waist
Also, if it's really chilly snuggish jeans have almost no insulation factor.
Don't worry, there are no fashion police except those who are self-appointed and you don't want to know them anyway.
Don't stress and have a great cruise !!!