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>

deploy/hooks/post-receive

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Install this at <bare-repo>.git/hooks/post-receive on your own Git server
+# (chmod +x it) and adjust DEPLOY_ROOT below. Pushing to `staging` deploys
+# to the staging checkout; pushing to `main` deploys to production.
+#
+#   git remote add origin <you>@<git-server>:/srv/git/bookstore.git
+#   git push origin staging
+#
+set -euo pipefail
+
+DEPLOY_ROOT="/srv/bookstore"
+
+while read -r oldrev newrev refname; do
+  branch="${refname#refs/heads/}"
+
+  case "$branch" in
+    staging)   target="$DEPLOY_ROOT/staging";    env="staging" ;;
+    main)      target="$DEPLOY_ROOT/production"; env="production" ;;
+    *)         echo "post-receive: ignoring push to $branch"; continue ;;
+  esac
+
+  echo "post-receive: deploying $branch -> $env ($target)"
+  mkdir -p "$target"
+  git --work-tree="$target" --git-dir="$(pwd)" checkout -f "$branch"
+  ( cd "$target" && ./deploy/deploy.sh "$env" )
+done