Expose R_LICENSE_KEY in Railway template

[mrubens]

Summary

• add the optional R_LICENSE_KEY input to the Railway API service
• share the configured value with the app services
• document Railway configuration and environment precedence

Why

The application already supports deployment-provided license keys, but the Railway template did not expose that setting. This completes deployment-template parity for Railway operators.

Validation

• pnpm deployment:validate
• repository pre-push checks

[roomote-roomote]

No new code issues found. See task

• deploy/railway/template.yaml:41 and deploy/railway/README.md:230: Update the remaining claims that R_APP_URL is the template's one optional deploy-time prompt. Adding R_LICENSE_KEY makes those source-of-truth and operator instructions contradictory; the same stale wording also remains at deploy/railway/template.yaml:160 and deploy/railway/README.md:325.

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