feat(mariadb): add mariadb lts compose files

- add compose/mariadb/docker-compose.yaml for mariadb:lts
- expose port 3306 and persist data with mariadb_data volume
- add compose/mariadb/.env.example with default init vars

compose/mariadb/.env.example

@@ -0,0 +1,16 @@
+# MariaDB — environment variables
+# Copy this file to .env and adjust values for your environment.
+
+# Root password.
+# The default is for local development only — always change for production.
+MARIADB_ROOT_PASSWORD=mariadb
+
+# Database created automatically on first start (default: mariadb).
+MARIADB_DATABASE=mariadb
+
+# Additional user created automatically on first start (default: mariadb).
+MARIADB_USER=mariadb
+
+# Password for the additional user.
+# The default is for local development only — always change for production.
+MARIADB_PASSWORD=mariadb