fix: use entrypoint script for prod container startup

YAML folded block scalar (>) was preserving newlines for more-indented
continuation lines, so gunicorn received no arguments and defaulted to
binding on 127.0.0.1:8000. Replace with an explicit entrypoint script
so all args are passed correctly.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

deploy/entrypoint.prod.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+set -e
+
+python manage.py tailwind install --no-input
+python manage.py tailwind build
+python manage.py migrate --noinput
+python manage.py collectstatic --noinput
+
+exec gunicorn config.wsgi:application \
+    --workers 3 \
+    --bind 0.0.0.0:8000 \
+    --access-logfile - \
+    --error-logfile - \
+    --capture-output