fix: add MySQL init script to create test database

Creates wordpress_unit_test database on MySQL container startup.
This ensures the test database exists before PHPUnit runs.

Author: josephfusco

.docker/mysql/00-create-test-db.sql

@@ -0,0 +1,5 @@
+-- Create test database for PHPUnit tests
+CREATE DATABASE IF NOT EXISTS wordpress_unit_test;
+GRANT ALL PRIVILEGES ON wordpress_unit_test.* TO 'root'@'%';
+GRANT ALL PRIVILEGES ON wordpress_unit_test.* TO 'wordpress'@'%';
+FLUSH PRIVILEGES;