Fix basic auth: use htpasswd instead of openssl passwd

openssl passwd -apr1 produces inconsistent output in nginx:alpine.
Switch to htpasswd from apache2-utils which is the standard tool.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-entrypoint.sh

@@ -7,7 +7,7 @@ if [ -z "$AUTH_USER" ] || [ -z "$AUTH_PASSWORD" ]; then
   exit 1
 fi
 
-echo "${AUTH_USER}:$(openssl passwd -apr1 "${AUTH_PASSWORD}")" > /etc/nginx/.htpasswd
+htpasswd -bc /etc/nginx/.htpasswd "${AUTH_USER}" "${AUTH_PASSWORD}"
 
 # Hand off to the official nginx entrypoint (runs envsubst on *.template files)
 exec /docker-entrypoint.sh "$@"