Trigger a redeploy of a Railway service programmatically via the public GraphQL API

Documented steps

1. Create an API token at railway.com/account/tokens. Account/workspace tokens use header 'Authorization: Bearer <token>'; project tokens use header 'Project-Access-Token: <token>' instead.
2. All calls are POST https://backboard.railway.com/graphql/v2 with Content-Type: application/json (endpoint per https://docs.railway.com/reference/public-api).
3. Get the service and environment IDs: query environment(id) { serviceInstances { edges { node { id serviceName } } } } or list projects to find them.
4. Redeploy the current build: mutation serviceInstanceRedeploy(serviceId: String!, environmentId: String!) — payload {"query":"mutation { serviceInstanceRedeploy(serviceId: \"<id>\", environmentId: \"<id>\") }"}. Docs: https://docs.railway.com/integrations/api/manage-services
5. To deploy a specific new commit instead, use serviceInstanceDeployV2(serviceId, environmentId, commitSha). To redeploy an exact prior deployment, use deploymentRedeploy(id) per https://docs.railway.com/integrations/api/manage-deployments
6. Poll deployment status via the deployments/latestDeployment queries; watch X-RateLimit-Remaining response headers.