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>

.env.example

@@ -0,0 +1,48 @@
+# Copy this to .env.dev / .env.staging / .env.production and fill in real
+# values for that environment. The filled-in files are gitignored — never
+# commit them. Same code everywhere; only these values differ (see
+# design doc §01, Environments & deployment).
+
+# --- Site ---
+# (WP_ENVIRONMENT_TYPE is NOT set here — it's hardcoded per environment in
+# docker-compose.{dev,staging,production}.yml so it can't go stale.)
+SITE_DOMAIN=staging.example.com
+SITE_URL=https://staging.example.com
+SITE_TITLE="Bookstore (staging)"
+
+# --- WordPress admin bootstrap (used only on first install) ---
+WP_ADMIN_USER=admin
+WP_ADMIN_PASSWORD=changeme
+WP_ADMIN_EMAIL=admin@example.com
+
+# --- Database ---
+DB_NAME=bookstore
+DB_USER=bookstore
+DB_PASSWORD=changeme
+DB_ROOT_PASSWORD=changeme
+WP_TABLE_PREFIX=wp_
+
+# --- Staging only: basic-auth wall + noindex ---
+# Generate the hash with:
+#   docker run --rm caddy:2-alpine caddy hash-password --plaintext 'your-password'
+STAGING_BASIC_AUTH_USER=staging
+STAGING_BASIC_AUTH_HASH=
+
+# --- Backups (deploy/backup.sh) ---
+BACKUP_DIR=./backups
+BACKUP_REMOTE=
+BACKUP_RETENTION_DAYS=14
+
+# --- Supplier adapters (design doc §04) ---
+# staging: gutenberg_test   production: booksrun,ingram
+ACTIVE_SUPPLIER_ADAPTERS=gutenberg_test
+BOOKSRUN_API_KEY=
+INGRAM_API_KEY=
+INGRAM_ACCOUNT_ID=
+
+# --- Payments (Helcim) ---
+HELCIM_API_TOKEN=
+HELCIM_ACCOUNT_ID=
+
+# --- Marketing ---
+MAILERLITE_API_KEY=