refactor(just): Give Just it's own programs/ module

"It's overkill to give every single package it's own nix module" yeah
probably. I do it so that I never have to guess where something's
configuration lives again. Just open up marleyos/ in lazyvim, hit
<space><space>, search for program, profit.

The only exception is stuff specific to programming languages, such as
language servers and aliases to php artisan. Those live under
languages/<language>. Eventually I'd like to make dev shells for each.

home/default.nix

@@ -45,10 +45,6 @@
   # Autostart wanted systemd services.
   systemd.user.startServices = true;
 
-  home.packages = with pkgs; [
-    just
-  ];
-
   imports = [
     ./appearance
     ./languages

home/programs/default.nix

@@ -11,6 +11,7 @@
     ./fzf.nix
     ./gh.nix
     ./hyfetch.nix
+    ./just.nix
     ./lazygit.nix
     ./less.nix
     ./man.nix

home/programs/just.nix

@@ -0,0 +1,6 @@
+{ pkgs, ... }:
+{
+  home.packages = with pkgs; [
+    just
+  ];
+}