feat: add Docker image, production server and health check

- Multi-stage Dockerfile on node:24-slim, non-root, healthcheck, /app/data volume
- server.mjs wraps the Astro handler with brotli/gzip compression,
  security headers and graceful SIGTERM shutdown (npm start)
- GET /api/health/ reports server and view-counter DB status
- Move build-only packages to devDependencies (smaller runtime image)
- docker-compose.yml as an alternative for Dokploy Compose

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.dockerignore

@@ -0,0 +1,15 @@
+node_modules
+dist
+.astro
+data
+.git
+.gitignore
+.env*
+.claude
+.vscode
+docs
+*.md
+!src/**/*.md
+!src/**/*.mdx
+Dockerfile
+docker-compose.yml