Add update script for Docker image management

This script updates Docker images, restarts containers, and cleans up old image layers.

update.sh

@@ -0,0 +1,30 @@
+#!/usr/bin/env bash
+# ~/docker/ai-image-gen/update.sh
+#
+# Run this manually when you have a specific reason to update.
+# Models and outputs are in named volumes — they are never touched.
+#
+# Usage:
+#   chmod +x update.sh   (once)
+#   ./update.sh          (when you want to update)
+
+set -euo pipefail
+cd "$(dirname "$0")"
+
+echo "==> Pulling latest images..."
+docker compose pull
+
+echo ""
+echo "==> Restarting containers with new images..."
+docker compose up -d --force-recreate
+
+echo ""
+echo "==> Cleaning up old image layers..."
+docker image prune -f
+
+echo ""
+echo "==> Done. Services:"
+echo "    Forge    → http://localhost:7860"
+echo "    InvokeAI → http://localhost:9090"
+echo ""
+echo "    Watch logs: docker compose logs -f"