Docker build cache: .dockerignore, cache mount, layer reorder, restart script

- .dockerignore: exclude node_modules/.git/tmp/data/logs
- Dockerfile: BuildKit cache mount for npm, --omit=dev at install, drop
  npm prune step
- Reorder layers: shared/src/frontend copy before build, server copy +
  better-sqlite3 rebuild after. Server/shared changes no longer invalidate
  frontend build layer unless shared (FE dep) changes
- Remove duplicate shared COPY in runtime stage (bundled in FE build)
- docker/restart.sh: stop + rebuild + start in one script

docker/restart.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# scripts/docker-restart.sh — rebuild + restart docker container.
+# Usage: ./scripts/docker-restart.sh
+set -euo pipefail
+cd "$(dirname "$0")/.."
+
+echo "=== stopping existing container ==="
+docker compose -f docker/docker-compose.yml down 2>/dev/null || true
+
+echo "=== rebuilding image ==="
+docker compose -f docker/docker-compose.yml build
+
+echo "=== starting container ==="
+docker compose -f docker/docker-compose.yml up -d
+
+echo "=== status ==="
+docker compose -f docker/docker-compose.yml ps
+
+echo ""
+echo "app: http://localhost:${PORT:-8080}"
+echo "logs: docker compose -f docker/docker-compose.yml logs -f"