fix(entrypoint): exec memcached so docker stop is graceful

entrypoint.sh ran memcached in the foreground under bash. bash as PID 1 has no
SIGTERM handler, so the kernel dropped docker stop's SIGTERM; docker waited the
full 10s timeout and SIGKILLed the container (exit 137). exec memcached so it
becomes PID 1; it installs its own SIGTERM/SIGINT handlers and exits at once.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/entrypoint.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 echo "Starting Memcached..."
 sleep 5
-/usr/bin/memcached -u memcached -l 0.0.0.0
-
-exit 0
+# exec so memcached replaces bash as PID 1. bash as PID 1 has no SIGTERM
+# handler, so the kernel dropped `docker stop`'s SIGTERM and docker SIGKILLed
+# the container after the full 10s timeout (exit 137). memcached installs its
+# own SIGTERM/SIGINT handlers, so as PID 1 it shuts down immediately.
+exec /usr/bin/memcached -u memcached -l 0.0.0.0