Set reasonable character limit for user bio

[dotmacro]

Problem

The text box for the user bio seems to accept an unlimited number of characters. (For reference, I gave up after ~500k characters.) Among other issues, this pushes the top of the unscrollable user info card off the top of the screen, hiding the profile photo and username. (Fortunately, payment info is unaffected because that's currently always at the bottom.)

Solution

Determine a reasonable character limit. (500?)
Limit the input to n characters.
Indicate the user has reached the char limit the same way we do elsewhere: an error with the text "Bio cannot exceed n characters."