Switch deploy pipeline to Gitea polling; fix env-parsing and volume-isolation bugs

- Replace the bare-repo post-receive hook with deploy/poll-deploy.sh: Gitea
  and the Docker hosts are separate machines, so each box polls its branch
  via host crontab instead of needing an exposed webhook receiver.
- Add Blocksy theme + Blocksy Companion auto-install to deploy.sh (free
  tier; the paid Book Store starter site still needs a manual license step).
- Fix deploy.sh/backup.sh/restore.sh sourcing .env files as bash: a bcrypt
  hash's `$2a$14$...` shape breaks under `set -u`. Replaced with
  deploy/lib/env.sh, a literal (non-executing) KEY=VALUE reader.
- Fix docker compose itself mangling the same kind of value: both
  `environment: ${VAR}` and `env_file:` run values through Compose's
  interpolation, which silently blanks `$identifier`-shaped substrings.
  The staging basic-auth hash is now rendered directly into the Caddyfile
  by deploy.sh, bypassing Compose's variable system entirely.
- Fix dev/staging/production silently sharing one Compose project (and
  therefore one db_data volume) by pinning an explicit -p per environment.
- cron and wordpress now share one environment anchor so they can't drift
  apart again (cron was silently missing WORDPRESS_CONFIG_EXTRA before).

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

deploy/backup.sh

@@ -8,16 +8,17 @@ REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 cd "$REPO_ROOT"
 
 ENV_FILE=".env.${ENVIRONMENT}"
-set -a
-# shellcheck disable=SC1090
-source "$ENV_FILE"
-set +a
+# shellcheck source=lib/env.sh
+source "$REPO_ROOT/deploy/lib/env.sh"
 
 TIMESTAMP="$(date +%Y%m%d-%H%M%S)"
+BACKUP_DIR="$(env_get "$ENV_FILE" BACKUP_DIR)"
+BACKUP_REMOTE="$(env_get "$ENV_FILE" BACKUP_REMOTE)"
+BACKUP_RETENTION_DAYS="$(env_get "$ENV_FILE" BACKUP_RETENTION_DAYS)"
 BACKUP_DIR="${BACKUP_DIR:-./backups}/${ENVIRONMENT}"
 mkdir -p "$BACKUP_DIR"
 
-COMPOSE="docker compose -f docker-compose.yml -f docker-compose.${ENVIRONMENT}.yml --env-file ${ENV_FILE}"
+COMPOSE="docker compose -p bookstore-${ENVIRONMENT} -f docker-compose.yml -f docker-compose.${ENVIRONMENT}.yml --env-file ${ENV_FILE}"
 
 echo "==> dumping database"
 $COMPOSE exec -T db sh -c "exec mysqldump -u\"\$MARIADB_USER\" -p\"\$MARIADB_PASSWORD\" \"\$MARIADB_DATABASE\"" \