deploy-remote: ensure quadlet unit dir exists for all handlers

dankserver's ~/.config/containers/systemd did not exist (no quadlet units
had ever been installed there); the dankserver media handlers cp'd into it
without mkdir -p, failing before touching any container.

scripts/deploy-remote.sh

@@ -408,6 +408,9 @@ build_compose_image() {
 }
 
 quadlet_unit_dir="$HOME/.config/containers/systemd"
+# dankserver's user manager had no systemd container generator dir before the
+# quadlet migration; every handler that installs a unit must find it present.
+mkdir -p "$quadlet_unit_dir"
 install_quadlet() {
     local service="$1"
     local source_dir="$2"