feat: add standalone output + postbuild script for Railway deploy
- output: 'standalone' for optimized Railway builds
- outputFileTracingIncludes for data/ directory
- postbuild copies .next/static, public, data into standalone dir
- start script changed to node .next/standalone/server.js
- removed Tailscale dev origin from allowedDevOrigins
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>