Add database health check dependency for WordPress

Ensure WordPress waits for MariaDB to be fully initialized before starting, preventing "Error establishing a database connection" during startup.

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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docker-compose.yml

@@ -4,6 +4,9 @@ services:
     restart: always
     expose:
       - 80
+    depends_on:
+      db:
+        condition: service_healthy
     environment:
       WORDPRESS_DB_HOST: db
       WORDPRESS_DB_USER: ${MYSQL_USER}