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.

system/default.nix

@@ -58,6 +58,14 @@ in
     ];
     environment.systemPackages = [ pkgs.git ];
 
+    # Caps Lock is a second Escape; Shift+Caps Lock still toggles Caps Lock.
+    services.xserver.xkb.layout = "us";
+    services.xserver.xkb.options = "caps:escape_shifted_capslock";
+
+    # Compile the console keymap from the layout above, so the remap holds on a
+    # bare TTY and not only under a graphical session.
+    console.useXkbConfig = true;
+
     # Primary user, in the wheel group. No password set here.
     users.users.${user.name} = {
       isNormalUser = true;