Fix flaky env.test.ts and add /health/ready integration tests

[robertocarlous]

Problem

tests/unit/config/env.test.ts fails locally when env is pre-populated; /health/ready has no coverage.

Acceptance criteria

• Isolate env module per test (reset modules / child process)
• Tests for 503 when subsystems not ready, 200 when all marked ready
• CI green on clean runner

[Emmy123222]

@Emmy123222 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Can i work on this ??

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Emmy123222 to this issue.

[drips-wave]

Congratulations, @Emmy123222! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @Emmy123222: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @Emmy123222 as part of the Stellar Wave Program's 5th Wave 🥳

😎 @Emmy123222: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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