Surface safe job-server status for operators

[brudex]

Proposed labels: enhancement, area:backend, area:docker, help wanted

Context

The job application exposes /jobs/status, while job registration lives in the
job runner and Compose health checks focus on liveness. Operators need a
minimal non-sensitive view of registered jobs and schedules that does not
confuse process readiness with successful job execution.

Suggested starting points

• job-app.js
• job-runner/index.js
• compose.yaml
• docs/development.md
• test/release-smoke.test.js and new focused tests under test/

Scope

Extend the status response with non-sensitive registered job names and
schedules, clearly distinguishing service readiness from execution health.
Document the response and test its shape.

Non-goals

• Do not expose environment configuration, database data, credentials, job
  payloads, user data, or internal error stacks.
• Do not change endpoint authentication/access policy or claim that a job has
  successfully run when only registration is known.

Acceptance criteria

• /jobs/status returns a stable, documented shape containing readiness and
  safe registered-job metadata.
• The response cannot reveal configuration values, credentials, payloads, or
  database details.
• Tests cover the response shape and retain the existing health behavior.
• Compose configuration remains valid.

Verification

1. Run npm test.
2. Run docker compose config --quiet.
3. Start the job app with safe local configuration where available and inspect
   /jobs/status; otherwise cover the handler with a focused test.
4. Run git diff --check.