Add a keyboard layout picker to the Omarchy menu

[thorrrr]

Omarchy's whole design is that you pick a setting from the shell, it applies
immediately, and the config files underneath get written for you. Monitors,
network, DNS, power profiles, audio, themes — all of it works that way.

Keyboard layout is the exception. It's the one setting where you're sent to open
input.lua and type the right XKB string by hand — and you have to already know
it's gb, not uk, not "British".

Could it work like everything else? Pick GB, or French, or German, from a list;
the file gets written for you.

Two reasons it matters more than most settings:

• It's the first thing a user needs and the one they're least equipped to fix,
  because half the symbols on their keyboard are in the wrong place while
  they're trying to fix it.
• If your password contains a character that moves between layouts, you can be
  locked out at first login with no idea why.

The existing bar widget doesn't cover it — it only appears once more than one
layout is configured, so someone sitting on a single wrong layout never sees it.