users/frontear: persist cache directory

This is a bit of a temporary catch-all because I need ~/.cache/yarn but I also feel a bit lazy out a better place for it right now.

users/frontear/home/default.nix

@@ -18,6 +18,13 @@
     "ssh" = "TERM= ssh";
   };
 
+  # TODO: this is a catch all for now because there's a few apps
+  # that dump quite a bit of large data here. Main culprit right
+  # now is `yarn`.
+  my.persist.directories = [
+    "~/.cache"
+  ];
+
   my.programs = {
     armcord.enable = true;