feat: add Railway deployment target

[PAMulligan]

Summary

Adds Railway as Nerva's fourth deployment target. Railway builds the service from the same hardened multi-stage Dockerfile as the Node.js target — so the runtime code is fully shared — and railway.toml (config-as-code) wires up the build, /health health check gating each deploy, start command, and restart policy. Managed PostgreSQL connects via Railway's reference variables.

Closes #31

Changes

• setup-project.sh --railway — reuses the node snippets and node-server Dockerfile/compose (Railway is a Node deployment), adds railway.toml + nixpacks.toml, writes an .env.example documenting Railway's ${{Postgres.DATABASE_URL}} reference-variable syntax, and generates README deployment instructions (project + PostgreSQL setup, Root Directory = api, service variables table, auto-deploy behavior, railway run pnpm db:migrate for migrations, Nixpacks alternative)
• templates/railway/
  • railway.toml — builder = "DOCKERFILE", healthcheckPath = "/health" (failing checks keep the previous deploy live), startCommand, ON_FAILURE restart policy, watch patterns; commented preDeployCommand with the dev-deps caveat
  • nixpacks.toml — pnpm + Node 22 toolchain pins and build/start commands, used when switching builder = "NIXPACKS"
• No deploy workflow — Railway auto-deploys the connected GitHub repo on push (its core feature), so unlike the Lambda target no GitHub Actions deploy template is needed
• CI — templates/railway added to the required-dirs check; no new snippets, so no new typecheck step
• Skills/config/docs — deployment-config-generator Step 2d (Railway config-as-code, env reference table, Root Directory reminder), schema-intake target union + interview option, pipeline.config.json railway block, target mentions across CLAUDE.md/README/onboarding/pipeline docs, railway npm keyword

Test plan

• bash -n + shellcheck (CI severity) on setup-project.sh; JSON validation of touched configs
• Both TOML templates parse cleanly (smol-toml), with builder/healthcheck/start values confirmed
• Generated a real --railway project: 20/20 Vitest tests pass; railway.toml, nixpacks.toml, Dockerfile, docker-compose.yml present; README contains the deployment instructions with literal ${{Postgres.DATABASE_URL}} references
• Regressions: --node dry-run contains zero Railway files and a real node run earlier this session passes tests; --lambda dry-run unchanged

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