cleanup panel/account.php

[simonLeary42]

• use JS instead of PHP for making the initial login shell selection
• inject PHP variables into JS on its own string declaration line
• use one showOrHideCustomLoginBox function for updates and initial state, rather than writing the same logic 3 times
• use value "Custom" everywhere rather than using "custom" internally and "Custom externally"

[simonLeary42]

tested:

• custom login box is visible only when "Custom" is selected in dropdowon
• correct dropdown option is selected based on value in LDAP for each default shell and a custom shell

Screen.Recording.2025-04-24.at.11.07.26.AM.mov