feat: redistribution toggle

[sbackend123]

Checklist

• I have read the coding guide.
• My change requires a documentation update, and I have done it.
• I have added tests to cover my changes.
• I have filled out the description and linked the related issues.

Description

• Adds PUT /redistribution so operators can enable/disable participation in new redistribution rounds without restarting the node.
• Exposes current toggle state as enabled on GET /redistributionstate.
• When disabled, the agent skips sample/commit for new rounds; an already committed round still proceeds through reveal/claim.

Open API Spec Version Changes (if applicable)

Motivation and Context (Optional)

Related Issue (Optional)

#5313

Screenshots (if appropriate):

AI Disclosure

• This PR contains code that has been generated by an LLM.
• I have reviewed the AI generated code thoroughly.
• I possess the technical expertise to responsibly review the code generated in this PR.