Add a documented health and readiness matrix for deployments

[robertocarlous]

Why
The project has several operational endpoints and checks, but operators still need a concise source of truth for what each health signal means and when to use it.

Acceptance criteria

• Document the purpose of each health endpoint.
• Document what dependencies each endpoint verifies.
• Include recommended use in local dev, CI, and production.

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!