feat: add Dockerfile for containerized deployment

Adds a production-ready Dockerfile based on node:24-alpine:
- Installs only runtime dependencies (docker-cli, curl)
- Runs as non-root `node` user
- Includes HEALTHCHECK for container orchestration
- Adds .dockerignore to keep image lean

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,6 @@
+.git
+.gitignore
+docs
+README.md
+RELEASE_NOTES.md
+install.sh

Dockerfile

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+FROM node:24-alpine
+
+RUN apk add --no-cache docker-cli curl
+
+WORKDIR /app
+
+COPY server.js index.html ./
+COPY scripts/ ./scripts/
+
+RUN chown -R node:node /app
+
+USER node
+
+ENV NODE_ENV=production
+ENV DASHBOARD_PORT=3001
+ENV DASHBOARD_ALLOW_HTTP=true
+
+EXPOSE 3001
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+  CMD curl -sf http://127.0.0.1:${DASHBOARD_PORT:-3001}/ || exit 1
+
+CMD ["node", "server.js"]