Fix MariaDB healthcheck failing on MariaDB 11.8

The 'healthcheck --su-mysql' binary isn't reliably available in
newer MariaDB images. Switch to 'mariadb-admin ping' which is
always present. Also add start_period and increase retries for
slow first-boot initialization on small VPS instances.

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

docker-compose.yml

@@ -82,10 +82,11 @@ services:
     networks:
       - websitebox_internal
     healthcheck:
-      test: ["CMD", "healthcheck", "--su-mysql", "--connect", "--innodb_initialized"]
-      interval: 30s
-      timeout: 10s
-      retries: 5
+      test: ["CMD", "mariadb-admin", "ping", "-h", "localhost", "-u", "root", "-p${DB_ROOT_PASSWORD}"]
+      interval: 10s
+      timeout: 5s
+      retries: 10
+      start_period: 30s
 
   certbot:
     image: certbot/certbot