docker: make the stack multi-instance so a test.escapepage.com copy can run alongside prod

compose.yaml / compose.override.yaml:
- container_name is now ${STACK_NAME:-escapepage}-* (STACK_NAME is a plain var,
  not COMPOSE_PROJECT_NAME, so prod keeps its escapepage-* names with no config change)
- every published host port is ${*_PORT:-<current default>}, so prod is unchanged
  and a second stack can bind its own (localhost-only) ports
- nginx joins the external nginx_default network so Nginx Proxy Manager can
  forward to <stack>-nginx by name

restart.sh:
- scoped to STACK_NAME / COMPOSE_PROJECT_NAME read from docker/.env, so running it
  from the test checkout can't touch the prod stack
- host-wide `docker system prune` / `docker builder prune` moved behind --prune-all

Adds docker/.env.test.example and doc/test-environment.md (separate checkout,
env layers, NPM proxy host + Access List IP allowlist, Mercure on test).

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

docker/restart.sh

@@ -1,22 +1,50 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
-# Script to completely restart the project as requested
-# Can be run from any directory
+# Completely restart ONE project stack (prod or a test/staging copy).
+# Can be run from any directory. Everything is scoped to the Compose project
+# name so running this from the test checkout never touches the prod stack.
+#
+#   ./docker/restart.sh              # rebuild-less restart of this checkout's stack
+#   ./docker/restart.sh --prune-all  # also run host-wide `docker system/builder prune`
+#                                    # (old behaviour; skip it when another stack shares the host)
 
 DOCKER_DIR=$(cd "$(dirname "$0")" && pwd)
 ROOT_DIR=$(cd "$DOCKER_DIR/.." && pwd)
 
-echo "Stopping and removing containers..."
-(cd "$DOCKER_DIR" && docker compose -f compose.yaml -f compose.override.yaml down -v --remove-orphans) || true
-docker network rm escapepage_network || true
-docker network rm $(docker network ls -q --filter name=escapepage) || true
-docker network prune -f || true
-docker rm -f escapepage-db escapepage-php escapepage-nginx escapepage-mercure escapepage-mailer escapepage-php-worker escapepage-php-cron || true
-docker system prune -f || true
+PRUNE_ALL=0
+for arg in "$@"; do
+  case "$arg" in
+    --prune-all) PRUNE_ALL=1 ;;
+    *) echo "Unknown option: $arg" >&2; exit 1 ;;
+  esac
+done
 
-echo "Clearing Docker build cache..."
-docker builder prune -af
+# Read the identifiers from docker/.env (same file Compose uses). STACK_NAME is
+# the container-name prefix; COMPOSE_PROJECT_NAME is the compose project.
+read_env() { [ -f "$DOCKER_DIR/.env" ] && grep -E "^$1=" "$DOCKER_DIR/.env" | tail -n1 | cut -d= -f2- | tr -d "\"'" || true; }
+STACK="$(read_env STACK_NAME)";            STACK="${STACK:-escapepage}"
+PROJECT="$(read_env COMPOSE_PROJECT_NAME)"; PROJECT="${PROJECT:-$STACK}"
+echo "Restarting stack: $STACK (compose project: $PROJECT)"
+
+echo "Stopping and removing containers..."
+(cd "$DOCKER_DIR" && docker compose -p "$PROJECT" -f compose.yaml -f compose.override.yaml down -v --remove-orphans) || true
+
+# Belt-and-suspenders: drop anything still lingering for THIS stack only.
+docker rm -f \
+  "${STACK}-db" "${STACK}-php" "${STACK}-nginx" "${STACK}-mercure" \
+  "${STACK}-mailer" "${STACK}-php-worker" "${STACK}-php-cron" 2>/dev/null || true
+for net in $(docker network ls -q --filter "name=^${PROJECT}_" 2>/dev/null); do
+  docker network rm "$net" || true
+done
+
+if [ "$PRUNE_ALL" -eq 1 ]; then
+  echo "Host-wide prune (containers, networks, build cache)..."
+  docker system prune -f || true
+  docker builder prune -af || true
+else
+  echo "Skipping host-wide prune (pass --prune-all to force it)."
+fi
 
 echo "Setting permissions for var/volumes/db and var directories..."
 sudo chown -R 1000:1000 "$ROOT_DIR/var/volumes/db" || true