yarn: fix impermiance home directory

system/impermanence.nix

@@ -21,12 +21,15 @@
       "/etc/ssh/ssh_host_rsa_key.pub"
       "/etc/machine-id"
     ];
+  };
 
-    users.${username} = {
-      directories = [
-        "."
-      ];
-    };
+  # Bind mount entire home directory from persistent storage
+  # (impermanence doesn't support "." so we do this directly)
+  fileSystems."/home/${username}" = {
+    device = "/persistent/home/${username}";
+    fsType = "none";
+    options = [ "bind" ];
+    neededForBoot = true;
   };
 
   systemd.tmpfiles.rules = [