Register, reset, and Steam-linking forms used a separate "Show
password" CheckButton row; the main login form already had the eye
icon embedded in the field itself. Generalized _add_password_reveal
(previously hardwired to a single tracked button) to support multiple
fields via password_reveal_entries, and used it for every password
field instead. Removed the now-unused _add_show_password.
Verified all 6 password fields (login, register x2, reset x2, steam)
get a working reveal button and there's no leftover "Show password"
checkbox anywhere.