Add Railway deployment target

[PAMulligan]

Description

Add Railway as a deployment target. Railway is a modern PaaS that auto-detects Dockerfiles and provides one-click PostgreSQL provisioning — a natural fit for Nerva's Node.js deployment path.

Why

Railway is increasingly popular among indie developers and startups for its simplicity. It auto-deploys from GitHub, provides managed PostgreSQL, and has a generous free tier. Adding it as a target lowers the barrier for deploying Nerva-generated APIs.

Acceptance Criteria

• Add `--railway` flag to `setup-project.sh`
• Create `templates/railway/` directory with:
  • `railway.toml` or `railway.json` configuration
  • `nixpacks.toml` if needed for build customization
• Configure health check, start command, and build command
• Generate appropriate environment variable references
• Update `deployment-config-generator` skill to support Railway
• Add deployment instructions to the generated project README
• CI passes

Resources

• Railway docs