feat: remap caps lock to escape on every host

Sets the xkb layout and `caps:escape_shifted_capslock` in the shared base
config, and builds the console keymap from it so the remap applies on a
bare TTY rather than only under a graphical session. Shift+Caps Lock
still toggles Caps Lock.

neogaia's `console.keyMap` is dropped: `console.useXkbConfig` defines
that option itself, so the two definitions would conflict.

hosts/neogaia/default.nix

@@ -39,5 +39,4 @@
 
   time.timeZone = "America/New_York";
   i18n.defaultLocale = "en_GB.UTF-8";
-  console.keyMap = "us";
 }