Switched the image from supervisord to s6-overlay because it provides a much smaller memory footprint.

s6-overlay vs supervisord — Memory Footprint Comparison

s6-overlay:
Uses only 1–2 MB of RAM. Its service processes typically consume around 200 KB RSS each.
Extremely lightweight, written in C, minimal overhead.

supervisord:
Consumes roughly 10–15 MB of RAM in real-world usage.
Implemented in Python, so it naturally has a higher baseline memory footprint (≈8–10× s6-overlay).

sing-box.sh

@@ -2308,6 +2308,7 @@ install_sing-box() {
   sing-box_variables
   [ -n "$PORT_NGINX" ] && check_nginx
   [ ! -d ${WORK_DIR}/logs ] && mkdir -p ${WORK_DIR}/logs
+  [ ! -d ${TEMP_DIR} ] && mkdir -p $TEMP_DIR
   ssl_certificate
   hint "\n $(text 2) " && wait
   sing-box_json