Add request body schema version header support

[Chucks1093]

Summary
Add request body schema version header support

Scope

• add response header indicating active request schema version\n- centralize version source in config/constants\n- document expected consumer behavior

Acceptance Criteria

• scoped change is implemented with no unrelated file churn
• docs/tests are updated where applicable
• contributor can validate the outcome locally

Contributor coordination: if you pick this up, reach out in Telegram for updates or clarification: https://t.me/accesslayerorg

[probablyABug]

@probablyABug has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

hi, i would like to work on this.

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[jotel-dev]

@jotel-dev has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

Please allow me to carry out this issue with a high level of precision, with an estimated completion time of 4 hours.

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[khanavi272-spec]

@khanavi272-spec has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

I would like to work on this issue

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[drips-wave]

Congratulations, @jotel-dev! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

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[drips-wave]

This issue has been completed by @jotel-dev as part of the Stellar Wave Program's 4th Wave 🥳

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