fix registration config disable

[goshacodes]

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[augmentcode]

🤖 Augment PR Summary

Summary: This PR fixes clearing a client registration configuration through the configuration API.

• Migrates affected Central configuration request handlers from zio-schema JSON decoding to zio-json codec decoding.
• This preserves the custom Option[Patch[A]] contract, where an explicit JSON null means delete rather than no change.
• Updates client creation and update handling along with other configuration mutation endpoints for consistent request decoding.
• Adds an integration-style controller test proving registrationFlow: null is forwarded as Some(Patch.Deleted).

Technical Notes: The change relies on each request model's derived JsonCodec and keeps the existing service-layer validation and response behavior unchanged.

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