No idea if 30 constitution (or higher) is possible. I just hit Ctrl+U, then looked at the `Nurture your own health` passage and got the values from there. I found the companion stuff on `Reset maximum companion number`.
I did Ctrl+F and found 17 times where constitution is increased by 1 point (not counting character creation but including the starting trait and hunger buff). I don't know if any of those are repeatable.