Add Docker development environment

Multistage Dockerfile (WooCommerce download, wp-bootstrap npm build,
Composer deps, WordPress runtime), Compose stack with MariaDB, and
auto-setup entrypoint that installs WordPress and activates the theme
on first boot.

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

docker/.env-dist

@@ -0,0 +1,19 @@
+# Database
+MYSQL_ROOT_PASSWORD=rootpass
+MYSQL_DATABASE=wordpress
+MYSQL_USER=wordpress
+MYSQL_PASSWORD=wordpress
+
+# WordPress
+WP_PORT=8080
+
+# Auto-setup (runs on first boot, set to 0 to disable)
+WP_AUTO_SETUP=1
+WP_URL=http://localhost:8080
+WP_TITLE=WC Bootstrap Dev
+WP_ADMIN_USER=admin
+WP_ADMIN_PASSWORD=admin
+WP_ADMIN_EMAIL=admin@example.com
+
+# Build args (used during `docker compose build`)
+# WOOCOMMERCE_VERSION=latest