Week 1 infrastructure: Docker environments, deploy pipeline, bookstore-core scaffold

Docker Compose environments for dev/staging/production (MariaDB, Redis,
Caddy, Action Scheduler cron sidecar), an idempotent deploy script,
git-hook-based deploy pipeline, backup/restore scripts, and the
bookstore-core plugin stub with WooCommerce HPOS compatibility declared.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker/cron/entrypoint.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+# System-cron replacement for Action Scheduler / WP-Cron (design doc §01).
+# WORDPRESS_CONFIG_EXTRA sets DISABLE_WP_CRON, so this loop is the only
+# thing driving scheduled events in every environment.
+set -eu
+
+echo "bookstore-core cron sidecar starting (60s interval)"
+
+while true; do
+  if ! wp cron event run --due-now --path=/var/www/html --allow-root 2>/tmp/cron-last-error.log; then
+    echo "cron run failed: $(cat /tmp/cron-last-error.log)"
+  fi
+  sleep 60
+done