beatific: Use programs.<prog> where available

Based on the option source, this doesn't actually change anything, but it seems like good practice in case it becomes necessary for another program or a future version of these.

modules/beatific.nix

@@ -75,14 +75,16 @@ in {
         curl
         duf
         file
-        git
-        htop
         nebula
         python3
         tree
         vim
         wget
       ];
+      programs = {
+        git.enable = true;
+        htop.enable = true;
+      };
       # The nixpkgs default is "nano", so we go one priority higher
       environment.variables.EDITOR = mkOverride 999 "vim";
     })