feat(shoukei): reduce size limit for root tmpfs

hosts/12kingdoms-shoukei/hardware-configuration.nix

@@ -100,7 +100,7 @@ in
     # set mode to 755, otherwise systemd will set it to 777, which cause problems.
     # relatime: Update inode access times relative to modify or change time.
     options = [
-      "size=4G"
+      "size=1G"
       "relatime"
       "mode=755"
     ];